Abstract: Introduces an engine fuel-film compensator realized through the analysis of fuel-film model transfer function meeting the nonlinear characteristics of air-fuel ratio in transient condition. A transient air-fuel ratio correction formula is proposed based on the engine temperature and the first-order throttle filter recursion. The method is used to control the fuel injection of a model 125 motorcycle. When correction of the transient air-fuel ratio control is adopted, it can be seen from the test data that the emission and fuel consumption of the engine are reduced and that the engine's running is smooth.