Abstract: The closed-loop proportional and integral feedback control strategy for air fuel ratio in an electronic control engine based on switch-type Exhaust Gas Oxygen(EGO) sensor is introduced in this paper, and the A/F ratio self-learning control strategy is analyzed in detail. Additionally, the necessity and reason and the relationship with closed-loop PI regulation, and enabling conditions of the A/F ratio self-learning control strategy are investigated. designs The main program and time delay subprogram algorithm for the self-learning control strategy based on switch-type EGO sensor are designed. Finally, the analysis of the A/F ratio self-learning control strategy is accomplished in theory level.