Abstarct: Miami Plain is one of the most important watersheds in Semnan province. In recent years, due to excessive withdrawal of groundwater resources, groundwater levels in the aquifer of the plain have fallen. For this reason, it is essential to consider the management of groundwater exploitation as a principle in water resource planning. In this study, the simulation of the aquifer of the Miami plain using GMS software has been done. The simulation of the aquifer was done using available data and information from the plain in the month of 2007 as the sustainable month. Also the data from October 2008 to October 2013 was used as the unstable state. baxsed on these data, the aquifer mathematical model of the plain was prepared and calibrated. The validation of the model was carried out using data from October 2013 to September 2017.The results of validation as well as statistical indices showed a high correlation between the simulated values of the model and the actual measured values. After verifying the model, in a scenario assuming the continuation of the current withdrawal of groundwater resources, the prediction of the groundwater level for the period of 2013-2017 was done. The results of the water level prediction showed that with the assumption of continuity the current water withdrawal from the aquifer, the groundwater level will fall from 1 to 5 meters in different parts of the aquifer. The highest drop will be in the central to northeast parts of the aquifer.