Inlet performance is an important field in aerodynamic design of aerial vehicle engines. This study has been focused on numerical investigation of Mach number effects on a supersonic axisymmetric mixed compression inlet performance. For this purpose, a density based finite volume CFD code has been developed. A structured multi-block grid and an explicit time discretization of Reynolds averaged Navier-Stokes (RANS) equations have been used. Furthermore, Roe’s approximated Riemann solver has been utilized for computing inviscid flux vectors. Also, the monotone upstream centered schemes for conservation laws (MUSCL) extrapolation with Van Albada limiter has been used to obtain second order accuracy. In addition, Spalart-Allmaras one-equation turbulence model has been used to close the governing equations. The code is validated in three test cases by comparing numerical results against experimental data. Finally, the code has been utilized for numerically simulation of a specific supersonic mixed compression inlet. The effects of free stream Mach number on performance parameters, including mass flow ratio (MFR), drag coefficient, total pressure recovery (TPR), and flow distortion (FD) have been discussed and investigated. Results show that Mach number increase, leads to TPR and drag coefficient decrease; however, MFR and FD increase. Also, FD variations with respect to other performance parameters are significant, such that Mach number increase from 1.8 to 2.2 leads to more than 100% FD increment while MFR has been increase less than 10%. By using this code, it will be possible to design, parametric study, and geometrical optimization of axisymmetric supersonic inlet.