Abstract: The specific capacity can evaluate the water rich property of aquifer and divide the hydrogeological type of mine water, we analyze the significance of conversion about specific capacity. Besides, we explain the method of using the Q-S curve equation to converse the pumping test data of three times, and how to deal with the data of one or two times drawdown. At last, the method was verified by use of the actual data of a coal mine, and the results are in accordance with the actual situation of the water rich property of aquifer.