Replacing gasoline vehicle by natural gas vehicles has advantages, such as lower CO2 emissions, and lower oil consumption. But this replacing faces significant challenges such as: lower traveled distance in comparison with vehicle gasoline, gas vehicle price is Higher than the vehicle gasoline price and as well as high investment costs in infrastructure section Such as gas stations. This paper by providing a dynamic system model, simulates and analyzes NGV fleet of long-term policies from 1390 to 1410 using vensim software. In this study, vehicles selection and Development of gas stations are two main elements of the model. In the vehicle selection between two types of car (gasoline and gas vehicle) from buyers characteristics such as vehicle price, number of stations, fuel costs and vehicle depreciation costs has been considered and modeled. The Result of study shows that the extension process of gas vehicles and number of stations will have increasing trend by assuming the continuation of the base year condition. so that NGV's share of total vehicles will reach to 27% and their numbers will reach approximately 10 million units With continuing situation of base year at the end of the year 1410 .The sensitivity analysis shows that the elimination of ration of gasoline and releasing prices of gasoline and gas have the Most effect on adoption of gas vehicles and following decreasing gasoline consumption.