Abstract: According to the special signal transmission requirements of the third-generation nuclear power plants, taking the tri-axial feedthrough as an example, and aiming at the special requirements of the tri-axial cables through the containment and its radio frequency signal transmission, this paper describes the design, manufacture, process test and type test of the special tri-axial feedthrough for the electrical penetration assembly. The results of the final type test show that the structure design of the tri-axial feedthrough is reasonable and the manufacturing process is feasible, which can meet the technical requirements of the electrical penetrator assembly in third-generation power plants, and its research results can be directly applied to the design of the electrical penetrator assembly for third-generation power plants.