Abstract: Injection-production ratio was determined in initial development stage can't be adapted in medium water cut period, in which formation pressure and liquids production were decreased year by year. Based on material balance and injection and production voidage balance and several methods (emphatically considered the effect of formation pressure decline on crude degasification and invalid rate of water injection), proper injection-production ratio in medium water cut period was determined which was 1.2. According to the study conclusion and the need to build up formation pressure, injection-production ratio was adjusted to more than 1.25 and better application effect was obtained. The study methods in this paper could be used for reference in similar oilfield.