A new kind of hydraulic motor suitable for the low velocity, large torque, high efficiency and mutable velocity output have been researched and developed in this paper. There are a series of creations and in advantage, such as, the oil flow distribution, the principle of reducer, the output mechanics and the total structure. It features in the simple in construction, small of size, large ratio of reducer, high f ratio of torque-power, and low in energy consumption. It is suitable for all the occasions with hydraulic supply and all the fields when low velocity, large torque, high efficiency and mutable velocity output ware needed. Such as the construction mechanics, ship mechanics, heavy machine tool, heavy capstan and so on. The frequency of the hydraulic system is about 1000—2000/min, the reduced ratio of the planetary drive of swinging bevel gear is about 20-100, with 150 the maximum. This paper introduced the fundamental principle of the transmission of this mechanics, designed the basic structure of this mechanics, and analyzed the movement and forces.