The research on the coupling electromagnetic effect was studied in this paper, in consideration of the wreaking damage of the powerful electromagnetic pulse to the electronic products. The characteristic of the metallic via and stub interconnect with the coupling voltage was calculated by the model, which was the transfer function F( f ) of the protection circuit parameters of DC power source. The research showed that: the smaller radius of Metallic via, the lower amplitude of F( f ), the less energy of a power electro- magnetic pulse (PEP); the higher increase of the width of the stub interconnect, the bigger reduction of the characteristic impedance of plane wave coupling, the depth of the notch band significantly narrowed. The simulations and experiments were done to compare the protection effects of protection circuits with different parameters at last. The results showed that the protection circuit designed could be highly advantageous in protecting the DC power source in this article.