Abstract: In order to evaluate the material shielding effectiveness（SE)on the effect of strong electromagnetic field，a new SE test method named shielding box method（SBM)was brought forward and the test system was introduced.The SE of one material was tested by different methods which include SBM，shielding room method and coaxial test method.The same results of the three methods show that the SBM is reasonable.The SE of energy selective surface（ESS)material was tested with SBM，and the test results indicate that the method is applicable for the strong electromagnetic environment.The relationship of SE and electric field strength，polarization direction can be analyzed by the method，which complements the shortcoming of shielding room method and coaxial flange method.