With the rapid development of the underground laying project of electric power cable, the higher requirement for the cable protection, the cable protection casing is made of polyethylene PE and high quality steel pipe after blasting blasting, impregnation or coating, and heating curing process. It is the most commonly used electrical insulating tube to protect wires and cables. Because of good insulation performance, high chemical stability, no rust, no aging, can adapt to harsh environment is widely used. The use of cable protection casing protection cable can achieve the following advantages: 1, good corrosion resistance, long service life, can be used in the humid saline-alkali zone. 2, flame-retardant, good heat resistance, can be used at 130 degrees of high temperature for a long time without deformation, the fire does not burn. 3. High strength and high rigidity. The construction progress of the high speed cable can be achieved without adding the concrete protective layer under the direct buried lane. 4, the cable protection casing, whether pipe or pipe fittings have a certain flexibility, can withstand the external pressure and foundation subsidence caused by damage. 5, has a good resistance to external signal interference performance. 6. Smooth inner wall and no scratch cable. The design uses the socket type connection way, facilitates installs the connection. The rubber sealing ring is suitable for the expansion and contraction of the joints and also prevents the mud sand from entering.