Abstract: With respect to serious misuse of the curves between cumulative water storage rate, water drive index and water cut in application, the derived theoretical relationship of such curves is presented by taking Type?C water drive curve as an example. Combined with actual development data from a low permeability reservoir in west China, changing rules of absolute and relative errors between misuse and real forecasting results with water cut are compared, when change of the accumulative injection?production ratio is big and water drive characteristic curve appears two straight segment. The results show that the misuse will result in that simultaneous solution between water-drive characteristic curve and cumulative water storage rate, water drive index is false