Abstract: Based on the abnormal trip of one domestic nuclear power plant reactor during the test of neutron flux measurement channels, Test scheme is established for the interference of the power source of the normal lighting system in the electrical building of the nuclear power station on the process instrumentation system, including the lights on/off interference test, the 220 V（AC） power supply box interference test, the safe distance between 220 V（AC） cable, process instrumentation system cabinet interference test and the cabinet ground check. Based on the test results, the causes of reactor trip is analyzed and the improvement program is proposed, including source term distance method, source term shielding method and grounding system correction. Some measures were verified that it can improve the ability of anti-electromagnetic interference.