1 Introduction The evaluation of the shielding effectiveness of thin metal shell, such as those of electronic device and equipment to electromagnetic pulse is essential for the electromagnetic compatibility (EMC) researches. The time response excited by an electromagnetic impulse is usually obtained by means of FFT techniques. It is understood easily in physical picture and suitable for the computation of time response excited by the slowly variant electromagnetic waves [I]. However, for most of electromagnetic impulse excitation, the sampling interval in time domain should be small enough to satisfy requirement of Nyquist's sampling principle, which leads to a bottleneck problem and restricts the application of FFT techniques to calculate the response of EMP to some extent. To deal with such problem, a fast approach to calculate time response of transient shielding effectiveness of cylindrical metal shell with an arbitrary transient excitation is proposed in this paper. The basic idea of the