In the past decades, many research and experiment on hybrid rocket propulsion has grown rapidly. Such rocket propulsion is considered as green propulsion system as the exhaust products cause less harm to the environment. Unlike solid rocket and liquid rocket propulsion, hybrid rocket propulsion takes the advantage that the fuel is in solid form while the oxidizer is in liquid or gaseous form. Any leakage of the oxidizer piping system will not result in undesired combustion from mixing between the fuel and oxidizer since the fuel and oxidizer needed to be effectively mixed for possible combustion. In this paper, the primary design consideration of the hybrid rocket motor is presented. Commercially available 3D printing material, Acrylonitrile Butadiene Styrene (ABS), and gaseous oxygen were selected as the fuel and oxidizer, respectively. The operation and performance of the hybrid rocket are highly affected by oxidizer injection into the combustion chamber. A proper oxidizer injector design is very crucial to avoid combustion instability for better performance of the rocket motor to be achieved. In this paper, the expected pressure drop of the injector for the designed hybrid rocket motor is higher than 7.5 bar as well as high oxygen gas recirculation in the pre-combustion chamber section is desired. The design of the oxygen gas injector for the hybrid rocket motor is done by using numerical design approach considering multiple orifices injector, radial injector and pintle injector. The simulation to observe the flow characteristic of each injector is carried out by using Solidworks Computational Fluid Dynamic (CFD) Simulation software. The parametric analysis on the output of the simulation, mainly the pressure drop of each injector, is carried out in searching for the optimal injector geometry. A good injector must satisfy the fuel regression rate with sufficient oxidizer mass flux rate along the solid fuel grain. The simulated oxidizer flow pattern is shown, and characterization of each injector is discussed. According to the simulation’s result, the multiple orifice axial injector has the highest pressure drop, 8.32 bar, among other two types for the same desired mass flow rate of 0.061 kg/s. On the other hand, the pintle injector can generate higher gas recirculation than axial injector while having the pressure drop of 6.25 bar, lower than the desired value of 7.5 bar. The pressure drop of radial injector stands in between axial and pintle injector, however this type of injector generates poor gas recirculation. Finally, according to the simulation result and analysis, the axial injector and radial injector are the potential designs to be selected for further study and develop for the designed hybrid rocket motor.