Abstract: The correlation-based γ-Re_θ transition model has been implemented into a large scale parallel compressible Navier-Stokes solver AHL3D. In order to simulate the effects of compressibility of the hypersonic flow, compressible modification has been added into this model. The constant parameter for the separation induced transition has been enhanced to improve the ability of the forced transition simulation. The correlation equations have been adjusted after all the modifications. In order to validate the modified models' ability to capture the transition location, a Ma=7.4 Ames all-body aircraft model for natural transition and a Ma=6 flat plate installed with three dimensional roughness elements for forced transition were simulated. The results show that compared to the original model, the modified model gives much later transition location and stronger effects of the roughness elements, which agree well with the experimental results. Finally, the modified model has been applied to the simulation of hypersonic natural and forced transition of the 20% scale X-51A fore body configuration in BAM6QT. The present model can simulate not only the effects of the free stream turbulence intensity but also the promotion of the transition position by the forced transition trips. The results show the good potential of the modified γ-Re_θ transition model in transition prediction for complex configurations in hypersonic flows.