Abstract: In order to study the electromagnetic disturbance brought by penetrative wire in power system under electromagnetic irradiation, a new method to calculate the coupling current of thin wire was derived with the equivalent voltage cell theory, which was improved to estimate the coupling current of thin penetrative wire within metal cavity. The coupling current distribution law was analyzed. The results show that, the penetrative wire response exists frequency selecting characteristic to electromagnetic irradiation, when the test wire electric length equals to semi-integer, the number of wave crest equals to n. Then an experimental plat was set up with a signal generator and current probe to analyze the coupling current for thin penetrative wire within metal cavity. The experimental results show the validity of the new method.