A test research has been made on the properties of the injector-pump. It is found that besides the area ratio and the distance between the jet-exit and the inlet of throat-duct, the obvious variation of pressure of the convergent part of the mixing chamber and the physical properties of the suctioned materials are also two main factors that should not be neglected. The theory of injector-pump has also been expounded. This paper presents the fundamental equation of jet pumps suitable for various cases. The factor of wall-Back-Force and a simple method for solving the momentum equation are also presented.