A novel explosive driven flyer initiation device with changeable velocity was designed. Flyer initiation tests with different densities PETN were finished and the history of velocity of flyer was observed by VISAR. Parameters of JWL EOS of PETN with different densities were calculated by VLW EOS. Velocities of flyer was simulated by the finite element hydrocode Ansys/Ls-dyna, which were coincided with results of tests. It testified feasibility of numerical method to calculate velocity of flyer. The relationships between flyer velocity and density of PETN were gained,so that the velocity of flyer could be adjusted from 2660 m?s^-1 to 3150 m?s^-1 with corresponding pressure range of 54-86 GPa.