In view of the narrow operating space of the screw joints, the smaller diameter of the pipe, the change of the pipe joint material, and the easy bending and deformation of the pipe in the electric propulsion system adopted by the DFH-3B platform satellite, the tightening sequence of each screw joint is optimized and optimized. Under the same other installation conditions, the tightening torque is proportional to the width of the sealing surface formed between the pipe ball head and the conical surface of the valve body. The author used ANSYS software to run a mechanical simulation test of Screw Joint. Considering the quality of the sealing surface alone, the wider the width of the sealing surface, the higher the relative sealing quality. The methods of pipe fixing and alignment, confirmation of proper tightening torque, design and production of torque wrenches adapted to the working conditions, etc., effectively solved the problem of tightening and sealing of screw joints of electric propulsion pipes, and were successfully applied in the original model. The screw joint is tightened in place at one time, and the leakage rate is all qualified.