Abstract: For effecting high-efficiency separation of coal and gangue, a study is made on the method for selection of the 3-degree-of-freedom servo motor-driven system of the series-parallel gangue sorting robot, based on the robot′s structure and working principle, as well as the mathematic model for displacement, speed, acceleration, torque, and equivalent inertia of the parallel mechanism, and the planning for the gangue sorting motion trajectory. Whereas, the changes and distribution of robot′s active joint velocity, torque, equivalent inertia and power during sorting process are calculated and analyzed. To address the issues regarding the variations of velocity, torque and equivalent inertia accordingly with the changes of configuration of the mechanism, the method for preliminary selecting the servo motor according to instantaneous power, and by reference to the gear′s reduction ratio determined by maximum joint speed and allowable motor speed, and the motor′s function verified by its torque characteristic curve, is proposed. It is pointed out that during the design process, a reducer with a large reduction ration should preferably be selected whenever possible for reducing motor′s load inertia ration and interference induced by inertia fluctuation, and enhancing system′s control response speed and operating stability. Results of testing and application show that the developed robot operates with a cyclic time of one second and its capable of imparting to a piece of gangue a lateral thrust force of up to 25 kg. By virtue of the advantages of the parallel mechanism, such as high sorting speed, simple and rigid structure, and large working space, the robot is particularly suitable for making high-efficiency sorting of gangue from coal, and has been incorporated into a number of coal cleaning systems for removal of large pieces of gangue. Practice shows it can work continuously in a stable manner. The work made in the paper may serve as a reference for the design of gangue sorting robot′s servo system.