A base unit circuit is selected to study the effects of a typical circuit under Electromagnetic Pulse(EMP) interference and research the methods of susceptibility forecasting with system identification theory based on simulation software PSPICE. According to system identification theory,a set of energy coupling circuit models is established by input and output data. The Goodness of Fit(GOF) between the predictive output and actual output achieves 98.5%,indicating that the model is suitable. The GOF is compared and its applicability is tested by changing the parameters of interference voltage. The results show that the peak and the trend of the output waveform of the model can approximate the actual output;the larger magnitude of the parameters changes,the lower the fit. To a certain extent,the approach can reflect the sensitivity of the circuit to the pulse interference,thus it can lay a foundation for exploring new method of predicting sensitivity of the circuit electromagnetic pulse effect.