Abstract: The Taizhou Formation reservoir in the Caoshe Oil Field of the Qintong Sag of the Northern Jiangsu Basin is a complex fault block reservoir.Border faults work as good barrier while internal ones are unbounded,resulting in communication of reservoirs.Injection of CO₂ in laboratory experiment obviously expands crude oil and reduces viscosity,hence is qualified for CO₂ miscible flooding.Before gas injection,there are many problems with flooding pattern of the Taizhou Formation reservoir.For example,the division of development series is too simple;interlayer contradicts with each other;well pattern in some region is not perfect;plane productions are unbalanced;and vertical production degrees are different,et al.Dynamic monitoring after CO₂ injection has proved that,gas entry profiles of gas injection well are improved;formation reaches the minimum miscibility pressure;heavy components in crude oils are produced;and production in the whole region is stable and advancing.