A numerical simulation method is presented for calculating two dimensional two-stage light-gas gun impacts to launch flier to hypervelocity.It uses the complex algorithm, concerned with the treatment of multi-materials, multi-interfaces, huge distortions and high density ratios etc. Basing on multi-fluid VOF and PPM methods, we develop the MFPPM2 shock wave physics code to simulate the Sandia hypervelocity impaction experimental confighuration model. Some results from the MFPPM2 are griven and appear to be in good agreement with those of the CTH code in Sandia Laboratory.