Wide-range engines require high-quality flow from their upstream inlets. This study designs a two-dimensional variable geometry inlet for RBCC engines and evaluates its flow field characteristics and aerodynamic performance through numerical simulations. Initially, a fixed-geometry inlet was designed at freestream Mach number is 6, numerical calculation results revealed significant hysteresis loops during acceleration/deceleration and low mass flow capture ratios in the low supersonic regime. Then based on this baseline, a variable geometry inlet was developed by adjusting the third-compression ramp in M0 = 2–4, this adjustment transitioned the inlet from an unstarted state to a started state. At M0 = 2, the total pressure recovery coefficient improved from 0.695 to 0.934, while the mass flow capture ratio increased from 0.153 to 0.561. Moreover, the performance comparison between adjustment strategies reveals that under identical M0, the stepwise adjusted configuration exhibits slightly superior aerodynamic performance compared to the continuous adjusted configuration. This work provides insights into the design and adjustment of wide-range two-dimensional variable geometry inlets.