Abstract: Siemens isolating switch is widely used in Zhejiang Province, whereas, there exsists in its manual manipulation box such problems as poor moistureproof and frequent damp defects, which threatens the normal operation of substation system equipment. Therefore, the solution to the moistureproof problem of Siemens isolating switch manual operation box would play a positive role in improving the safety and stability of substation equipment operation. The original design of the manual box of Siemens isolating switch is analyzed, and the relevant improvement measures are put forward from the aspects of water discharge, moisture convection and box sealing, in hoping to provide positive help to solve the manual box damp problem.