Electricity energy was wasted greatly for light load and low efficiency of beam pumping unit system used in oil field. So, the vector variable frequency speed regulating technology is studied to adjust the rotational speed of oil-field motor dynamically. So that it can be adjusted according to the load of pumping unit. And closed-loop controller of pumping unit system was designed by adjusting motor speed. Design and implementation for pumping unit system of Fuzzy PIcontroller optimized by GA is proposed in this paper. The simulation research in Simulink shows that dynamic of speed control and fast start-up performance are improved, overshoot is suppressed effectively, and it has stronger adaptability and better effect.