The invention provides a method for discriminating cavity structure periphery electromagnetic environment strength. According to ship design scheme, a ship platform is established in a commercial electromagnetic field simulation software, according to relationship of near far field at the periphery of radiating antenna on the basis of electromagnetic theory, correlation of all the parameters of scatter and the radiating antenna as well as the cavity is constructed, thus primarily judging in which region of the radiating antenna the cavity is located in the shortwave full frequency range of working frequency of radiating antenna; if one part of the cavity is in far field region and the other part is in near field region, the field region of the radiating antenna where the cavity is locatedis further judged according to frequency of cavity electromagnetic effect. The invention estimates electromagnetic environment strength near cavity structure composed of sensitive devices at the periphery of strong radiation source and provides a reference frame for electromagnetic safety design and electromagnetic protection design of sensitive devices.