Abstract: Bolt residual torque is a critical factor influencing the sealing integrity of transmission housings. Process parameters such as the initial run-down speed, contact torque, transition torque, transition speed, and final tightening speed significantly affect the bolt residual torque. To optimize these parameters for transmission housing assembly, a 5-factor, 3-level orthogonal experiment was designed. Based on the orthogonal test data, the optimal parameter combination was identified through range analysis, followed by trial assembly verification of the optimized bolt tightening process. The results indicate that the sensitivity of factors affecting the sealing performance at the transmission housing joint surface is in the following order initial run-down speed > transition speed > transition torque > contact torque > final tightening speed. Notably, the final tightening speed has a negligible impact on bolt residual torque and can be set as a fixed parameter. The optimal combination for the remaining four parameters is an initial run-down speed of 285 r/min, contact torque of 9 N·m, transition torque of 15 N·m, and transition speed of 55 r/min. This parameter set effectively meets the sealing requirements for transmission assembly.