Abstract: Based on the thermodynamics, a group of physical equations describing the relationship between the system internal energy and the electron density of hypervelocity impact generated plasmas were derived by combining with the chemical reaction rate equation. This group of equations was solved by a self-developed 2D SPH (Smoothed Particle Hydrodynamics) code to calculate the plasmas generated in the simulations of hypervelocity impacts in order to achieve the simulation of the generated plasmas. Then an aluminum projectile impact on double plates was numerically investigated and the results were compared with some experimental results. After accounting the charges generated by impacts on the front plate and the back plate respectively, it was found that the charges generated by the impact on the front plate were much less than thoses generated by the impact of first debris cloud on the back plate. Another simulation under the same condition except for the exchange of the two plates was conducted and the result showed that the plasma charges generated by the impact of debris cloud on the back plate in this simulation were less than that in the previous simulation but the plasma charges generated by the impact on the front plate in this simulation were more than that in the previous simulation. From these simulations, it could be concluded that the plasma charges generated by hypervelocity impact were not only related to the projectile mass and the impact velocity but also closely dependent on the thickness of the thin plate. The collision between the debris cloud and the second target generated more charges than the impact on the single target by the projectile. The impact on double plates increased the generation rate of the plasma and electromagnetic damage to the spacecraft.