Abstract: In the research on flow and heat transfer of the diesel engine cooling system, the boundary condition is often difficult to be determined. The paper made a whole heat transfer modeling calculation for solid-fluid coupled system which contained the piston-liner-coolant-cylinder body in a six-cylinder diesel engine, which could omit the definition of the boundary condition when they were calculated separately. Comparison the temperature between calculated results and measured values at some spots along with the axis direction on cylinder face was made, and the influence of simulation precision with different grids density was studied. Considering the computer resources and calculation precision, temperature field, flow field and pressure field of cooling system were obtained through simulating, which could provide guidance for engine design.