Increasing crop production is necessary to maintain food security for the growing global population. Reducing the gap between actual and potential yield is one of the important ways to increase yield per unit area. Potential yield and the yield gap of soybean were determined for Golestan Province, Iran, using Soybean Simulation Model (SSM-iCrop2) and Geographical Information System (GIS). Information from 24 weather stations and soil data of the region were used. Yield gap and production gap were calculated at county and province levels. The average actual yield of soybean in this province was 2.28 t ha–1 while the province's potential yield was 4.73 t ha–1, so the yield gap was estimated 2.44 t ha–1. Thus, there is a great potential for increasing soybean yield in Golestan, which is possible through improving crop management of soybean in farmers' fields. The average water productivity of soybean was estimated to be 0.81 kg m–3. Spatial distribution of water productivity in soybean farms showed that the highest and the lowest water productivities (0.99 and 0.44 kg m–3) were in western and eastern regions of the province, respectively, in accordance to vapour pressure deficit. It was concluded that soybean production in the province could increase by 66％ (from 109970 to 182170 tons) if 80％ of the current yield gap could be removed.