Abstract: The evolution of a planar heavy/light gas interface (SF₆/N₂) subjected to a perturbed shock wave produced by diffracting a planar incident shock over a rigid cylinder is investigated, focusing particularly on the incident impact of Mach reflection wave configuration. While the incident planar shock wave Mach number is 1.8, numerical schlieren images of the Mach reflection wave are provided, and the wave evolution during the incident impact on the heavy/light interface is quantitatively analyzed. Based on numerical simulations, the refraction process is analyzed and resolved using the three-shock theory, which appears to predict accurately the post-refraction shock wave shape, as well as the velocity perturbation and circulation deposition on the interface. Additionally, by drawing shock polar curves and rarefaction wave characteristic lines, the pressure changes and flow deflection across the wave configuration during the incident impact process are vividly described. Both the theoretical analysis and numerical simulation results indicate that differences in shock intensity and incident angles within the Mach reflection wave configuration induce velocity perturbation on the interface. The tangential velocity caused by the shock impact results in circulation deposition on the interface. Velocity perturbation and circulation deposition dominate the early evolution of the heavy/light interface.