Taking a typical gasoline engine cylinder head,cylinder gasket and cylinder block composite structure as an example,the working conditions of gasoline engine were simulated by using finite element analysis platform of ANSYS Workbench,and the fluid field,transient temperature field and transient structure field were analyzed by using the multiphysical field coupling analysis method.The flow velocity of gasoline engine cooling fluid,the temperature and stress of the composite structure and the deformation of cylinder gasket were obtained,and the effect of thermal load and mechanical load on the sealing performance of gasoline engine was discussed.Results show that the equivalent stress of the combustion chamber is larger and its change is more obvious under the action of thermal load and mechanical load,and the embossing deformation of the cylinder mouth is also obvious.The equivalent stress can be reduced by adjusting the of combustion chamber and the flow velocity of cooling fluid,and the deformation of cylinder gasket can be reduced by adjusting the embossing structure of cylinder gasket and the pretightening force of bolt,so as to improve the sealing performance of the gasoline engine.