A new type of camshaft connecting-rod low speed high torque (LSHT) hydraulic motor providing continuously variable displacement is presented in this paper. On the base of traditional LSHT hydraulic motor with dual displacement, a continuously variable displacement mechanism, which is composed of a hydraulic control valve with mechanical-positional feedback to camshaft, is designed for the traditional LSHT hydraulic motor. So the cam ring on camshaft of the traditional LSHT hydraulic motor can stop at any position between minimum and maximum eccentricity, according to an input fluid pressure signal or an input electric control signal, and can stay anywhere stabilized through self-adjusting. The new type of continuously variable displacement mechanism is simple, stable and easy to be made. Firstly, the structure and principle of the continuously variable displacement mechanism is introduced in this paper. Secondly, the mathematic model is set up.