Abstract: Communication between surface and bottom hole is the key technology for automatic control of well trajectory, which is one of the main focuses in drilling engineering at home and abroad. As an effective means of signal transmission, drilling fluid pulse becomes more and more popular, yet little study has been done on its transmission mechanism. This paper presents a mathematical model for the transmission system of drilling fluid pulse signal, with its solution met hod and examples also given. The study is beneficial for the improvement of available transmission system, and the development of new system as well.