In the process of cable laying on site, the phenomenon of scratch and damage on the surface of cable sheath is common, and only the sheath is damaged slightly. How to repair can ensure the quality, short repair time and ensure the quality has increasingly become a common concern of cable consumers. Moreover, the investment is small and easy to realize under the bad conditions on site. Therefore, the repair technology and quality of on-site sheath have increasingly become the concern of users. The on-site construction conditions of cables are generally poor, which may be located in the power plant under preliminary construction, the newly-built field railway under preliminary construction, on the bridge or in the cable tunnel. Because the repair of field cable sheath is carried out with plastic welding gun, and the heating of plastic welding gun requires 220V AC, it is in the emerging field project, Generally, there is a lack of power supply on site, or there may be power supply. Due to the randomness of the laying position of on-site cables, it is difficult to provide power supply. Therefore, to repair the cable sheath, on the one hand, the personnel are in place, on the other hand, the power supply is mainly provided. Only the above two basic preparations can be made, In order to realize the normal development and progress of cable sheath repair. In order to facilitate the smooth repair of cable sheath field, the construction unit shall be equipped with field small generators. At the same time, it is convenient for on-site repair. The quality of the plastic welding gun provided now should be excellent. The heating area of the nozzle should be large and the heating speed should be fast. Moreover, the damaged parts in the cable setting out process are random. This work is easy to carry out in general cities and plain areas, but in some mountainous areas, due to the influence of complex terrain, the cable repair work is actually very difficult. Therefore, in order to reduce the investment in corresponding aspects and quickly solve the problem, a key problem is that the number of personnel in the cable laying process must be sufficient, and formal cable laying equipment shall be used for formal setting out, so as to avoid and reduce the damage of sheath in the cable setting out process. The technology required for on-site cable repair is not very high. After the cable is damaged, the cable laying construction unit must repair the cable on the premise of confirming that there is no damage inside the cable, otherwise the cable sheath repair has little practical significance. The cable must be repaired in time, otherwise the entry of external moisture and moisture will affect the service life of the cable. In Meiyu weather in the south, after the cable end is laid, the cable end is not sealed in time, resulting in the water flowing into the cable trench entering the cable end for 10-20 meters. After stripping the insulation of the end, it is found that all the conductors have been blackened, resulting in the waste of the cable after laying. Therefore, the inspection of the cable after laying should be strengthened, Maintenance and storage shall be carried out to prevent the shortening and termination of cable life caused by various external factors on site before power on. Some tools and materials used for on-site repair of cables must be fully prepared. Plastic welding gun is necessary. High voltage insulating tape, waterproof tape, peeled leather of plastic insulation and sheath, and other sealing materials must also be prepared, because cable insulation and sheath materials are mainly divided into cross-linked polyethylene, polyethylene, polyvinyl chloride and other materials. Some materials are thermosetting materials, such as cross-linked polyethylene insulation, which cannot be melted and reused again. They can only be repaired with high-voltage insulating tape and repair tape series provided by 3M company in the United States. Some materials belong to thermoplastic materials, which can be melted and used again at high temperature, such as polyethylene, polyvinyl chloride and other materials. Some materials can be taken on site, and the corner sheath material stripped from the cable end can be cut into thin strips to repair the insulation and sheath of low-voltage cables, The repair quality can fully meet the requirements of the normal service performance of the cable. In addition, the treatment of sheath damage of medium voltage cable during on-site laying should not be too rough. One is that the cable must be handled with care during the laying process. In addition, after the external damage of the cable, the damage of its internal insulation is sometimes hard to say, The author once conducted a return test on the cables with multiple damaged outer sheath caused by careless construction in the field laying process, and found that partial discharge exceeded the standard and breakdown occurred in the damaged parts of the cables. Therefore, for medium voltage power cables with damaged outer sheath in the field laying process, it is best to cut off the intermediate joint or replace the cable again, Because there may be hidden dangers after repairing the damaged part of the cable. Facts have proved that the repair of insulation and sheath of low-voltage cables must be slightly damaged. The repair of insulation and sheath can only be carried out on the premise that the insulation and sheath are damaged and other structures of cables are intact. The requirements of medium and high-voltage cables may be more stringent. In order to reduce the number of intermediate joints of cables in cable transmission of some projects now, All cables are long-length single core cables. Due to the long laying distance of the line, responsible terrain, the number of construction personnel and the lack of professional cable laying equipment, the probability of cable sheath damage during the construction process is greatly increased. After the above problems occur in some construction, it is irresponsible to wrap a bag of ordinary tape casually. There is no knowledge of the internal damage of the cable damage point. Insulation breakdown or potential quality hazards are likely to occur during the on-site completion test and later operation of the cable.