Abstract: When the analog channel test of reactor protection system(T1 test) in Qinshan Phase Ⅱ Nuclear Power Plant, the transient fault of the unit was caused by the failure of the switch. In this paper, based on the transient fault caused by the switch fault during the test, the switch body is analyzed, and the method of switch switching verification is proposed. Combined with the work practice, the optimized maintenance strategy is put forward, which effectively ensures the safe and stable operation of the unit.