Recently, the hybrid rocket propulsion has become attractive to the research community and has developed the trend to become an alternative to the conventional liquid and solid rockets. The hybrid rocket is a combination of both the solid and liquid systems with half of the plumbing of the liquid rocket but retaining its operational flexibility and avoiding the explosive nature of the solid rocket. Among available hybrid systems, the N2O (Nitrous Oxide)-HTPB (Hydroxyl-Terminated PolyButadiene) hybrid propulsion represents the simplest but sufficiently efficient design. Unfortunately, even until now, research in developing hybrid N2O-HTPB propulsion system still strongly depends on trials-and-errors, which are time-consuming and expensive. Thus, detailed understanding of the fundamental combustion processes that are involved in the N2O-HTPB propulsion system can greatly impact the research community in this field. This may further facilitate the successful modeling of the combustion processes and help improving the design of N2O-HTPB propulsion system in the future. A comprehensive numerical model with real-fluid properties and finite-rate chemistry was developed in this research to predict the combustion flowfield inside a N2O-HTPB hybrid rocket system. Good numerical predictions as compared to experimental data are also presented.