Abstract: Drill-string is the important channel of EM-MWD (Electromagnetic measurement while drilling) signal transmission. The influence of drill-string can not be ignored when evaluating the transmission effect of EM-MWD signal transmission. Therefore, the finite element method is employed to simulate the characteristics of EM-MWD signal transmission. To analyze the influence laws of factor on EM-MWD signal transmission, which includes the cross-sectional area of annulus, the cross-sectional area of drill-string, the resistivity of drill-string and insulation nipple position through ground current density and ground receiver voltage. The simulation results show that signal intensity will be increased with the increase of drill-string cross-sectional area and the distance between drill bit and insulation nipple, but has nothing to do with annulus cross-sectional area. Signal intensity will be increased with the drill-string resistivity.