In order to study the dynamic mechanical property of aluminum alloy for amphibious aircraft, dynamic tensile tests were carried out by using an electronic universal tensile test machine and high velocity test system at room temperature. The stress-strain curves of 7475-T761 and 7055-T76511 aluminum alloy of seaplane bilge structure were obtained under strain rate between 0.005~500 s-1, and Johnson-Cook constitutive model was fitted and verified. The results show that the strain rate hardening effect of 7475-T761 and 7055-T76511 aluminum alloy is obvious under strain rate between 0.005~500 s-1, and the failure strain increases with the increase of strain rate. 7475-T761 aluminum alloy has a certain strain hardening effect, but 7055-T76511 aluminum alloy has a weak strain hardening effect. The fracture morphology of two aluminum alloys shows no obvious necking phenomenon. The fitted John-Cook constitutive model can well characterize the dynamic mechanical properties of two aluminum alloys, and the maximum root mean square error is 13.7 MPa.