Lean burn technology shows great potential in meeting the more strict emission regulation and realizing high efficiency and clean combustion. In this paper, a feedforward-feedback control system of the air-fuel ratio controlling for lean burn engine is presented. A fuzzy parameter self-tuning PID control scheme is used as feedback to balance the control accuracy and system complexity. Some lean burn engine air-fuel ratio control experiments are given to show the efficiency of the proposed method. With the proposed control system, the the actual engine air-fuel ratio can quickly track the desired air-fuel ratio when the engine load changes suddenly regardless of whether the target air-fuel ratio is 20 or 14.6. So, the fuzzy parameter self-tuning PID controller has excellent control performance under transient condition of lean burn engine.