Due to the significant impact of the injectors on the efficiency and durability of the engine, the design and simulation of the injector is very important. In this paper at first the design and computation of a swirl injector with spiral paths is proposed. The injector is designed in such a way that it has an open spraying angle and very low layer thickness which is suitable for limiting the length of the chamber and provides a finer powder. Since the phenomenon of creating and developing an air cavity in the internal flow of injectors and simulating it which is due to the presence of two turbulent twist currents in two different phases with a common free surface is complicated, the internal flow has a potential effect on the spray properties of the swirl injectors. Therefore, in the next step, simulation of the internal flow of the injector with two different fluids (water and kerosene) has been investigated and parameters such as spray angle, discharge coefficient, speed coefficient, spray film thickness, and average diameter of the droplets have been investigated. The Fluent® software is used for the present simulation and for a two-phase flow, the volume of fluid (VOF) method is considered. Further to these, the flow turbulence is simulated with the RNG model. since the results of the simulation have a very small error with design hypotheses, the results of simulation can be used in various industrial applications, especially in the turbine engines industry with the aim of reducing costs.