Abstract: A negative correlation between mean cross-sectional area and mean velocity of water flow had been established and tested by regressing mean sectional area and mean velocity of water flow monthly by using the data that were measured over a period of 12 months in the central water sump of one mine. The result showed that the higher of the mean cross sectional area is, the lower of the velocity of water flow is, and inversely, the lower of the mean cross sectional area is, the higher of the velocity of water flow is. Using water inflow, which obtained by calculating the observed data, divided by the product of mean regression area of cross sectional area timing the velocity of water flow, the corrected float coefficient of water inflow could be got. This corrected float coefficient makes the water inflow more approximate to the observed one.