The control system of boost CNG Engine based on electronic pressure regulator was studied. The structure and working principle of universal exhaust gas oxygen sensor were analyzed. Based on the main chip MPC561 and integrated CJ125, universal exhaust oxygen sensor control circuit and heater circuit were designed. Based on adaptive algorithm, the A/F ratio closed controller was designed and its control strategy of air-fuel closed loop was discussed. The CNG engine experiments of air-fuel ratio closed loop on bench test showed that the dynamic response of UEGO control system was rapid and accurate. Based on UEGO control system, the intelligent control of engine’s air-fuel ratio could be achieved, and the performance of economy and emission could be improved.