Abstract: Heihe Watershed is located in drought region with severe water shortage. The vegetation of its natural oases has been deteriorated rapidly and its ecological environment is facing a grim situation. The Miami Model and a correction method worked out by the authors were used for calculation and for predicting the distribution tendency of the biological yield of the Watershed. The results of the study are of practically valuable to the rational utilization of water and soil resources and to the protection of ecological environment of Heihe Watershed as well as the Northwest drought regions of China.