The coupled process between Electromagnetic Pulse(EMP) and Printed Circuit Boards (PCB) circuit in a shielding cavity is very complicated. At present, the existing studies have some limitations, namely lacking effective method which can combine the field analysis with circuit analysis. The coupled voltage is simulated on a microstrip line circuit within a shielding cavity by using a hybrid simulation method. Using electromagnetic topology model and Baum-Liu-Tesche(BLT) equation, this method calculates the coupled voltage caused by the EMP. The results show that the coupled voltage is about 1.5 V when the strength of the EMP reaches1 000 V/m. The effects on the PCB circuits caused by the incident EMP are calculated and simulated using the circuit simulation software. The signal-amplified circuit cannot run normally when the strength of EMP is up to 300 V/m.