Abstract: EM-MWD(Electromagnetic-measurement while drilling) develops rapidly because it can not be af-fected by drilling fluid.The main reason limiting its development and application now is that the distance the elec-tromagnetic wave can reach is not deep enough.This paper mainly discusses the method of calculating the trans-mission channel of electromagnetic MWD system-effective transmission line method.Several factors possibly affecting the quality of electromagnetic wave transmission were discussed.The paper can mainly be divided into two parts:theoretical part and experimental part.The impacts of antenna parameters,excitation frequency on the voltage were discussed in the theoretical part.And the influence of the length of the metal ring on the voltage was proved in the experimental part.Through the analysis of various factors,engineering and technical personnel can use the effective transmission line method to choose rational incentives used by the device size parameters,which are optimized for the purpose of the antenna size.Based on the data collected,a number of deficiencies in the process of theoretical analysis were given.