Increasing concentrations of greenhouse gases, increase the frequency of precipitation changes in all around the world. So, identification of the effect of global warming on precipitation of Iran which located in dry area is important in planning to water resources. According to aim of this study, statistical analysis has been used. Total precipitation data of 34 selective stations during 1984 to 2018 were obtained from Iran meteorology organization. In addition, data of methane gas (in billions in part) as one of most important factors of global warming were obtained from NOAA website. At first, correlation between these parameters identified by using Pearson correlation coefficient, then precipitation changes rate were calculated compared to long term. The results show that, spring precipitation in north and northwest of Iran have a growth about 13 mm, and precipitation in southern part of Iran has decreased by 46 percent compared to the long-term. Due to increasing of greenhouse gases, the results of data analysis on summer show decreasing about 30 mm of precipitation of southern stations of Iran compared to long term. But, precipitation of north and west stations of Iran, have a growth about 14 mm. In addition, results show that fall precipitation has highest correlation with global warming. In this season, precipitation of west stations decreases about 24 mm compared to long term. But the southwest and southeast stations have an increasing about 17 mm. The results of data analysis on winter precipitation show decreasing about 18.6 mm on west and northwest stations of Iran.