Abstract: Aiming at the problems of large spatial and temporal scale and low precision in current analysis of basin water scarcity, a method suitable for the study of water scarcity in data-deficient watersheds was established, using the SWAT model to calculate the total amount of water resources of the watershed. Based on the statistical data, the water demand of the watershed was calculated, and the monthly change characteristics of water scarcity in the watershed studied. The method was applied to Mangxi River Basin, with the characteristics of water shortage being analyzed from perspectives of different time, different space and different industries. The results showed that the annual average total water resource in Mangxi River Basin was 564.6 million m³, the available water was 105.99 million m³, the total water demand was 126.5 million m³, and the water scarcity was 31.34 million m³. Affected by rainfall and agricultural irrigation, the water scarcity in Mangxi River Basin was mainly in the dry season, especially in April and May when the agricultural irrigation needs were the greatest.