In view of the characteristic that the bottom pressure of Coalbed Methane Wells (CBM wells) is low and the structure of coal bed could be easily destructed, the author designed a kind of jet pump. The jet pump could improve efficiency of washing bottom-hole coal particle in condition of protecting the structure of coal reservoir. In this paper, we have analyzed the structure of jet pump and working principle; and given the method of calculation the basic parameters of jet pump on the basis of calculating the working efficiency of jet pump from the point of cavitation.