Abstract: The sealing performance directly affects the normal use of steam traps and causes serious steam waste. To prevent the steam leakage, it is necessary to ensure that the traps have good sealing performance. This article focuses on the theoretical analysis of the steam trap flange gasket bolt sealing system, obtains the calculation formula for bolt pretightening force, and provides a method to control the pretightening force. By controlling the bolt pretightening force, the sealing effect of the steam trap bolt connection can be improved.