The thermal balance of the engine is an important basis for analyzing and evaluating the design state,especial-ly the performance of the cooling system,and is an important basis for the continuous optimization of the engine.Compared with the test evaluation under vehicle condition,the engine bench test has the advantages of complete working condition,convenient and reliable control.Combining with the practice of a gasoline engine,this paper provides a complete evaluation method of engine thermal balance composition through test analysis,which has a good engineering application effect.