Electromagnetic measurement while drilling（EM-MWD）is a new technology in present petroleum drilling, which is applied in directional drilling in big oilfields in China. According to the low resistivity in petroleum formation, serious electromagnetic wave signal attenuation and limited surveying depth in construction process, assumption was put forward to design a small diameter EM-MWD system for solid deposit of high-resistivity formation and shallow drilling depth. The paper analyzed the technical requirements and the feasibility of EM-MWD.