The shock-wave velocity can be obtained with two-sensitivity method on the measurement of shock-wave velocity with imaging velocity interferometric system for any reflector (VISAR) . Since the decision difference for shock-wave velocity, the velocity curve may be not unique. This problem will be serious due to the effect of speckle and decrease of fringe pattern. The new method for target design is provided. After comparing the area of shock-wave velocity and the thickness of transparent window, the shock-wave velocity can be confirmed. And the uncertainty of VISAR system can be achieved which is agreement with the theoretical prediction. This method, which presents the shock wave velocity and uncertainty of VISAR, provides the new way for accurate diagnosis by VISAR system.