Abstract Theory and numerical computation of EM field distribution rule in a biological medium with irregular shape are described. Integral equations on induced EM field distribution in biological body are deduced from EM field scattering. Numerical computations are conducted by the moment method. In order to verify effectiveness of the theory, a set of experimental equipment i? designed precisely. The results of numerical computation are compared with measured values. It is shown that they are agree very well. This theory can be used widely for its generality.