Applications of geographic information systems (GIS) and remote sensing to estimate runoff of watersheds have increased in recent years. In this research, runoff curve number map of Birjand Mansourabad watershed was prepared by GIS data and Landsat ETM+ satellite images based on factors such as hydrologic for soil group, land use and land cover. The land cover map was determined using Normalized Difference Vegetation Index (NDVI) and VI Index and was classified as three groups: good, fair and poor. The watershed land use map was produced by Landsat satellite data and hydrologic soil group map was produced using field survey, watershed soil, slope, geology and land use maps. The combination of these maps in GIS and using SCS table, runoff curve number and soil surface store Coefficient maps was obtained. Several rainfall-run off events were used to evaluate the accuracy of the result. It was found that predicted peak discharge using HEC-HMS model is similar to the observed peak discharge which indicates that the predicted result is reasonably accurate. On the other hand curve number obtained of observed flood data was compared with curve number computed by the model with error analysis of RMSE= 3.57 and MRE=0.5 showing that the obtained results are accurate.