Abstract: Based on the wreaking damage of the powerful electromagnetic pulse to the electronic products, the coupling voltage on the power line and the protection circuit were studied in this paper. The coupling voltage's range was calculated by the model. Based on the coupling voltage's range, the protection circuit of DC power source was designed. The protection circuit was composed of transient protection circuit and low-pass filter. The transient protection circuit was designed to reduce the amplitude of the interference signal and discharge a part of interference signal energy. The low pass filter was designed to filter out the high frequency components. The simulations and experiments were done to compare the protection effects of protection circuits with different parameters at last. The results show that the protection circuit designed in this article can protect the DC power source very well.