Abstract: A method for analyzing electrical excitation mode of electromagnetic measurement while drilling (EM-MWD) is proposed. By this method, a lot of calculations for EM-MWD has been done, and some very important data have been obtained, in which the electric field intensity distribution patterns on the earth s surface, the dependent relations of electric field intensity upon the frequency and the input impedance of the transmission equipment are included. All of the calculated results agree well with that of the laboratory test and the shallow well test.