Particular landform of Tacheng Region allows water vapor from the west, so as to form many medium- and small-sized rivers. The seasonal snow covers the hills. During the snow-melting season in spring, the rivers have the character of spring flood, which makes uneven distribution of annual runoff and results in a disadvantaged allocation of water resources. This paper established an annual runoff model of BP neural network for the Wulasitai River in Tacheng Region, according to the characteristic of the annual runoff changing. The forecasting results show that the model has good adaptability and precision.