Abstract: In this paper, our main concern is the effects of the mitigation layer in the underwater explosion problem. As the explosive gaseous products, water, mitigation layer, and so on constitute a fluid mixture, the physical states of these components are covered by a uniform Mie-Grüneisen equation of states(EOS). Then the Mie-Grüneisen mixture model is applied to simulate the complicated interaction among gaseous product, water and solid layer. In the calculation, the particular parameters of EOS are used to make a distinction among the physical properties of fluid components and the volume fractions are used to identify the interfaces. In addition, the inlet and outlet boundary conditions are implemented here. During the calculation process, the effect of the mitigation layer is investigated here. According to the investigation, it is found that the effect of the layer is decided by the shock impedance of layer material. The pressure of the shock wave will decrease when it penetrates a new medium with lower impedance. On the other side, the penetrated shock wave in the layer is reflected by the structure and produces a second shock wave. During this process, the affection of layer thickness and distance is also studied here. But both two factors are unimportant under the mitigation mechanism.