Abstract: Aim To design a closed loop knock control system (KCS) in order to improve the power and economy of spark ignition (SI) engine, while preventing engine from knock. Methods A resonance type knock sensor and a peak value recorder circuit were used to detect engine knock, a two parameter ignition angle adjusting method was adopted, a closed loop knock control system was designed, and the knock limits were optimized by experiments. Results and Conclusion The experiments show that the design of the hard and software and ignition angle control strategy are feasible, the power and economy of the engine are improved.