In order to prevent and control the water inflow of mines, this paper built a new initial GM(1, 1) model to forecast the maximum water inflow according to the principle of new information. The effect of the new initial GM(1, 1) model is not ideal by the concrete example. Then according to the principle of making the sum of the squares of the difference between the calculated sequences and the original sequences, an optimized GM(1, 1) model was established. The result shows that this method is a new prediction method which can predict the maximum water inflow accurately. It not only conforms to the guideline of prevention primarily, but also provides reference standards to managers on making prevention measures.