In order to clarify the characteristics of front and displacement efficiency of CO2 flooding in Fan142 Block，Zhenglizhuang Oilfield，a numerical simulation method for CO2 flooding and the optimization for well open sequence for oil wells are studied. A fully-implicit reservoir numerical simulator for CO2 flooding is developed by using the multiphase percolation theory and the numerical solution technique. Combining the geological/production data analysis and oil reservoir simulation，the distribution of CO2 and the displacement front of the block are studied during the pressure build-up stage by continuous CO2 injection. It is found that an obvious fingering phenomenon occurs at the CO2 flooding front. After 2 years of injection，the front has reached Well F142-6-2. The shortest distances from the front to Well F142-6-3 and F141-1-1 are 52 m and 45 m，respectively. The best scheme is that wells F142-8-3 and F142-7-3 in the low pressure area are first opened and the remaining 4 wells are opened for production after 1 year. The cumulative production for 5 years of this scheme is 1.34% higher than that of the scheme that the wells are opened at the same time，and the increase of oil production is 5 407 t. By comparing the oil recoveries，geological sequestration rates and replacement rates of CO2，it is indicated that the sequence of well opening have an significant effect on the displacement efficiency.