Greentel Fiber Closure are an indispensable part of fiber optic cable communications. Its main function is to realize the connection of fiber optic cable, and at the same time, to ensure the grounding function of the fiber optic splice closure, the internal grounding device and the grounding portion of the optical cable must be electrically connected, and the metal component and grounding device of the fiber splice closure and the fiber cable reinforcement core must be guaranteed. They are insulated from each other to avoid adverse effects from the environment on the fiber optic splice closures. Fiber optic splice closures, like fiber optic cables, have their own quality and play a vital role in the transmission of communications. Since the environment in which fiber optic splice closures are used is basically outdoor, their use environment may be buried, overhead, or pipeline. In order to prevent the impact of lightning or other factors, it is required that the“voltage withstand strength”of the fiber optic splice closure must comply with the requirement of no breakdown and no arcing within 1 minute after applying a 15 kV DC voltage in the standard. Therefore, higher requirements are placed on the design of the fixing and grounding device of the fiber optic splice closure and the insulating materials used. The key problem that most easily causes the failure of "withstanding voltage strength" in the fiber optic splice closure is that the distance between the two ends of the fiber optic splice closure or between the poles and the ground is too small. The dielectric strength of the uniform air at room temperature is 3 Mv/m. Therefore, to meet the requirements for no breakdown at 15 kV DC, the space between the two poles or between the pole and the ground should be at least 5 mm. According to the standard, the fiber optic splice closures must be soaked in 1.5 m deep water for 24 hours before being subjected to a voltage proof strength test. Therefore, if the seal is not good, water vapour infiltration will inevitably affect the withstand voltage strength performance.