The waterflooding and replacing oil is currently the chief method of enhancing oil recovery in the single well fracture-vuggy units in Tahe oilfield. But, the proportion of failure wells increases gradually, and then it influences greatly the effect of waterflooding performance. Through analyzing the mechanism of water injection for oil to improve the development effect and combined with the production characteristics, the main failures can be summarized. The main characteristics that may cause the wells ineffective are, the watercut rising quickly, the upturned of cyclic water injection instruction curve, the gradually decrease of the cyclic water storage rate, the dramatically increase of the cyclic water replacing for a ton of oil. For the water injection wells, the main objective causes accounting for the failure are: reservoir type of individual well and bottom water intrusion in late stage of water injection to replace oil; and too much injection of cyclic water injection in wells, and inappropriate cyclic injection production parameters caused by insufficient soaking subjectively.