Abstract: The theoretical research of electromagnetic measurement while driuing(EMMWD) transmission can contribute to instrument development and promotion. One driving mode is selected after comparing several types of driving mode. A theoretical model is set up based on the uniform medium transmission line model, combining the subtransmission line theory. The correctness of this theoretical model is proved by theoretical calculation and field test. The channel characteristics is analyzed, and the analysis result shows that formation resistivity, unit resistance of drill pipe length and working frquency are the main factors affecting the signal transmission.