This study was conducted by installing internal step components to improve the fluid flow and unstable mass flow caused by the internal flow line of natural gas injector. The experimental model has designed four different models depending on the location of the internal step components in the injector. The study method modelled the internal flow line of the injector and used the CFX(computational fluid program) to the analysis of fluid. As a result of the study, the model designed by the step component on valve seat secured a stabilized mass flow at the initial section of the stroke and the model designed by the guide line secured a high mass flow rate at the last section of the stroke. As a conclusion, A model with two step components could achieve an effective mass flow rate.