With a focus on a heavy diesel engine, complete set of multi-field coupling methodology aimed at analyzing and optimizing for fatigue-strength of cylinder head is proposed. A detailed model of the engine consisting of both the coolant galleries and the surrounding metal components is employed in both fluid-dynamic and structural analyses to accurately mimic the influence of the thermo-mechanical load on the cylinder head and block structural reliability. This model carries out several simulating experiments like 3-dimensional CFD of in-cylinder combustion and engine cooling jacket, simulation of cylinder head temperature field which use fluid-structure interaction, stress and strain analysis under thermal-mechanical coupling conditions and high cycle fatigue analysis. In order to assess a proper CFD setup useful for the optimization, the experimentally measured temperature distribution within the engine head is compared to the CFD forecasts. The analysis shows that computed temperatures were consistent with experimental measurements, and the danger region predicts through calculation matches the crack in actual experiment. In addition, the simulation analyzes two optimization schemes for problems of original head. The results show that the stress at the crack decreased from 245MPa to 230MPa after increased wall thickness, and the stress drop significantly after changed the cylinder material from gray iron to compacted graphite iron. Either increasing the wall thickness or replacing the material solved the crack failure obvious.