Abstract: According to certain block of Jilin oilfield, the displacement efficiency in different composite reservoirs has been studied with numerical simulation. The result of numerical simulation shows that when water drives oil, the displacement efficiency of positive composite reservoir is the highest, followed by homogeneous reservoir and inverted composite reservoir. When gas-alternating-water flooding goes, among three reservoirs, the displacement efficiency of homogeneous reservoir is the highest, followed by positive composite reservoir and inverted composite reservoir. Therefore, when water flooding develops, positive composite reservoir should be given priority. Moreover, inject wells should be in low permeability zone, while production wells should be in high permeability zone. When reservoir is stimulated, the producer should enhance the permeability near production wells. When gas-alternating-water flooding develops, homogeneous reservoir or the reservoir whose coefficient of anisotropy is lower should be given priority, followed by positive composite reservoir. These results not only play a very important role in plot optimization and reservoir stimulation also provide theoretical basis for field implementation of CO2 flooding.