Abstract: A digital controller based on digital signal processor (DSP) and field programmable gate array (FPGA) was designed to solve the problem of high precision and low velocity of large telescope ac servo system drove by permanent magnet synchronous motor (PMSM). A DSP was used as primary controller to perform the function such as computing control algorithm and receiving instructions. A FPGA was used as secondary controller to achieve the function such as PWM generation, current sampling and speed acquisition. Mathematic model of PMSM was found based on vector control, and hardware of PMSM digital controller was designed. The large telescope table was tested at low speed through employing adaptive PI controller after completing the controller hardware design. The experiment results demonstrate that when the large telescope table run at 32.4 ()/s, the range of velocity fluctuation is 0.648 ()/s; when the large telescope run in the mode of sine guide, which is with the maximum velocity 1 ()/s and maximum acceleration 1 ()/s2. The maximum guide error is 9.72 , and the value of RMS error is 3.24. The drive control system can realize high precision control of large telescope and meet the need of system performance.