The mount drive control is the key technique which mostly affects astronomical telescope’s resolution and its speed. However, the ultra -lower speed and the giant moment of inertia make it very difficult to be controlled. In this paper, one segmented permanent-magnet synchronous motor (PMSM), 4m diameter, is suggested for the mount driving. A method is presented to drive the motor direct ly, which is based on TMS320F28XX and Insulated Gate Bipolar Transistor (IGBT) , also, HEIDENHAIN tape is used to detect the absolute position of the motor together with the Hall sensor. The segmented PMSM can work stable and the mount drive can realize nice tracking performance at ultra -lower speed with this drive system.