Due to the presence of air intakes outside the body of some missiles with research objectives as well as some unmanned aerial, the use of the air intake duct in S-shaped is necessary and therefore the air flow quality must be determined, with the most important parameters being the total drop and distortion is from the beginning of the air intake until the delivery phase to the engine. In this research, it has been determined that the optimum air intake geometry is determined according to the dimensions of a unmanned aerial. Therefore, we first tried to optimize the geometry of S-shaped air intake and then optimize this geometry based on the reduction of total pressure drop. The computational grid with ICEM software and mesh analysis by computational fluid dynamics (Fluent software) has been done. Given that the intake of unmanned aerial was considered in this study, Mach flight is considered 0.3. Since the output section is actually the same section of the motor, whose cross section is constant, it has been considered in optimizing the inlet section and the wall. By optimizing geometry, the total pressure drop dropped to about half. Given the fact that the optimization repetition resulted in undesirable changes in geometry, optimization of geometry was not repeated. Additionally, by comparing the optimized geometry with the initial geometry, It is known that the slow rotation of the flow (the lower rotation angle) reduces the total pressure drop and reduces the amount of distortion. In the end, the results of the numerical solution with the experimental results presented by NASA have been investigated, which indicates that the numerical solution is desirable.