Cavity flow represents a prevalent aerodynamic phenomenon in aircraft design, characterized by complex unsteady features including shear layer oscillations, boundary layer separation, vortex dynamics, and shock wave/expansion wave interactions. This study investigates Mach number effects on cavity flow characteristics through numerical simulations across a broad velocity range (subsonic to supersonic) for a cavity with length-to-depth ratio 7.0. Results demonstrate that for this conventional cavity geometry, the flow regime consistently exhibits an open cavity configuration. Distinct flow mechanisms emerge: subsonic conditions feature large-scale vortex-shear layer interactions, while supersonic flows manifest coupled shock wave-vortex-shear layer dynamics. Analysis reveals that subsonic/transonic flows exhibit enhanced shear layer perturbations and amplified pressure coefficient fluctuations at the cavity floor, attributable to lower freestream energy levels. Conversely, supersonic conditions with higher energy freestreams promote rapid shear layer traversal across the cavity opening, yielding reduced pressure fluctuations. Notably, while the cavity floor pressure coefficient decreases monotonically with increasing Mach number, the corresponding pressure load demonstrates a progressive augmentation. These findings offer critical insights for optimizing high-speed cavity designs in aerospace applications.