Along with the development of microelectronic process, it is possible to integrate a big system in one chip. A new way to implement system on a chip is provided by the advent of FPGA. Based on Verilog HDL and the Actel Fusion AFS600 FPGA chip, the speed closed-loop control system of DC motor was designed by using options of combining the top-down thinking and the bottom-up method. PID control algorithm, encoder signal processing and PWM waveform generation etc were realized by the system. The results show that the system structure is simplified and the stability and reliability are improved. A solution of system on a chip is realized to some extent. It has extensive application value in engineering practice.