Taking the fully floating piston of a marine diesel engine as the research object,a model by coupling multi-flexible body dynamics and thermo-elasto-hydrodynamic lubrication（TEHL）theory was established.Simulations were conducted at varied propulsion operation conditions while changing the inner diameter of the piston pin and the stiffness of pin seat in order to clarify the impact of these parameters on lubrication characteristics.The results reveals that with the increase of local stiffness of piston pin seat,the minimum oil film thickness and the time proportion of perfect lubrication state of piston pin seat bearing increases,thereby enhances the overall lubrication performance.