In the dynamic analysis and prediction of water drive oilfield，water drive curve can be used to predict water cut and recoverable reserves and evaluate dynamic development of oilfields. Through literature research and case study of oilfield，the survey found that Yu Qitai water drive curve was more convenient and accurate on predicting oilfield water cut. In the paper of A new method for prediction of volumetric sweep efficiency in water-drive oilfield，the authors deduced a new formula of predicting the volumetric sweep efficiency based on Yu Qitai water drive curve. However，irrationality existed in the process of its derivation，it was modified in this study and a revised one was proposed. Using the development data from T21 fault block in Shengtuo oilfield，the results of the two formulas，curves showing correlation between volumetric sweep efficiency and water cut，were respectively compared with that of Chen Yuanqian’s formula derived from Type-A，Type-B and Type-C water drive curves. The result of the revised formula has very good consistency with that of Chen Yuanqian’s formula；but the result of the original formula is different from that of Chen Yuanqian’s formula，which shows its irrationality. The revised formula is not only more widely applicable for different field types，but has more reasonable and accurate calculation result，and should be popularized.