In order to solve the difficulty of determining boundary conditions when calculating heat transfer between single parts in diesel engines, outer boundary condition can be transformed to inner boundary condition using coupled heat transfer method, so that heat transfer simulation can conform with the actual working mode, using software to build models and simulate. As an example, piston-cylinder liner of X6130 diesel engine was modeled by FEM software named ANSYS. After simulating transient cyclic heat transfer in rated wording mode, transient temperature curves of piston-cylinder liner key points were gotten. Comparison between simulation data and measurement shows that coupled method is feasible to simulate piston-cylinder liner heat transfer, and simulation results are in good agreement with experimental data.