Abstract: Based on the functional requirements of shielded twisted-pair(STP) cable penetrating containment, and combined with the environmental conditions of the third-generation NPPs, this paper developed a STP feedthrough for electrical penetration assembly(EPA), which is specially used for connecting STP cables inside and outside of the containment. This paper focuses on the overall structure design, material selection and type test of STP feedthrough. Through a series of type tests, it is proved that the STP feedthrough has good sealing performance, electrical performance, irradiation resistance and electromagnetic compatibility. The test results show that the STP assembly meets the expected design requirements of specified design life, sealing and electricity.