In this paper, we use numerical modeling (Groundwater Modeling System) and mineable coefficient method to calculate the groundwater allowable exploitation amount of Guanghua basin, so as to rationally evaluate and analyze regional groundwater resources and exploitable potential, and to prevent groundwater overexploitation and the resulting geological disasters. The results show that the 3D numerical model of groundwater flow this paper constructed can provide a reasonable groundwater flow simulation result for the study area. In 730 days of the entire simulation period, the root of standardized residuals of 60th, 180th, 540th and 730th days respectively were 4.996%, 4.043%, 6.517% and 6.787%. Taking the maximum depth of water level of 5m as a constraint condition of water extraction in karst aquifers, the groundwater allowable exploitation amount is 12997.78×104m3 by the numerical model calculation. The groundwater allowable exploitation amount in Guanghua basin is 14015.10×104m3 with the method of mineable coefficient method. The relative error of the results calculated by numerical modeling and the mineable coefficient method is 7.3%. The two methods are verified by each other, and the results are reliable. On the basis of the above, the objectives and measures of the groundwater management for the emergency reserve water source of the Guanghua basin are put forward.