Using suitable coordinate systems in CFD have been of interest for many researchers. The objective of this study is numerical modeling of supersonic flows, using a new coordinate system, i.e. Unified coordinate system (UCS) and Iterative Riemann problem solution. Unified coordinate system has advantage over traditional coordinate systems (Eulerian/Lagrangian) in supersonic flows, especially in discontinuous regions (shocks and expansions). Moreover, most of the difficulties of the traditional coordinate system may be removed using UCS. For 2-D gas dynamics calculations in UCS, it is required to approximate fluxes on cell faces. This is normally modeled by Riemann problem solution. It is important to mention that in using UCS, there is no need to generate a body-fitted mesh prior to computing flow past a body, the grid is automatically generated by the flow. The UCS has the advantages of both Eulerian and Lagrangian systems. These can be seen in our results, which also show the high speed in our computations.