In order to figure out the mechanical response of bridge deck pavement with cracks，under internal dynamic water pressure，using the LS-DYNA finite element analysis software，a model of asphalt pavement with crack was established to analyze the stress state of crack. The results showed that under the action of vehicle dynamic load，the maximum pressure and shear stress of the micro cracks are located at the crack tip，while the maximum tensile stress is located around the crack；the maximum pressure and shear stress have a good linear correlation with the vehicle speed and load level，in the case of 120 km/h velocity and 1.5 MPa load level，the maximum X direction,Y direction pressure and shear stress respectively reach to 0.472 MPa,1.101 MPa and 0.361 MPa,under which micro cracks will expand rapidly. The main factor leading to the expansion of the water filled micro cracks in asphalt pavement is the overloading of vehicles,so the traffic management department should strictly limit the overloading of vehicles.