Abstract: Aiming at the fractal and gray characteristics of time sequence of mine water inflow, R/S analysis was used to determine Hurst index and average cycle period of time sequence of mine water inflow, the equal-dimension gray filling dynamic prediction model GM(1,1) was set up with a cycle. The up-to-date information was fully used to improve the prediction accuracy of the model. GM(1,1) model based on R/S analysis was applied to predict the inflow in a mine in Northern Shaanxi Province. The result showed that the model had good fitting degree and high prediction accuracy, and it could provide decision basis for safe production in mines.