In order to study the influence of mechanical constraints and thermal state on thermoelastic contact nonlinear problem that between cylinder head and cylinder head gasket， a four-body contact simplified model of cylinder head-cylinder head gasket-engine block-bolts was built based on a four-valve diesel engine. Under different bolt preload and thermal state， contact state and deformation of cylinder head plate were calculated by using Augmented Lagrange multipliers as the contact algorithm. Then the influence of contact stresses and nodal displacements of mechanical constraints on some parts of the cylinder head plate were revealed in rated thermal state condition. Moreover the effect of different thermal state on the results was similarly revealed. The study makes clear that， when preload maintains the rated value and burst pressure is exerted， contact stresses in rated thermal state condition of the parts on cylinder head plate that against the cylinder ring and around the screw， which is on exhaust valve side， are similar with those values in cold state， while nodal displacements are reduced， and in different thermal states， the rates of change among the nodal displacements around the screw and both contact stresses and nodal displacements that against the cylinder ring are all less than 2%; with few exceptions， contact stresses and nodal displacements of these parts of the cylinder head plate increase with the increases of the bolt preload. The results also show that cylinder head gasket sealing tests in normal temperature condition is roughly adequate to practical state.