The invention relates to a method for optimizing CO2 injection rate to increase the recovery ratio through CO2 displacement of reservoir oil and belongs to the technical field of recovery ratio increase through CO2 displacement of reservoir oil. The method comprises the following steps: firstly, establishing a target block three-dimensional geologic model; establishing the relationship between the CO2 injection rate and the increment oil exchanging ratio through the numerical simulation method according to the target block three-dimensional geologic model; by combining the target block, increasing the optimal increment oil exchanging ratio determined by the economic boundary index of a recovery ratio project, and optimizing the optimal CO2 injection rate of the target block. According to the method, the increment change rule of the oil production after CO2 injection is fully taken into consideration, and the optimal injection rate obtained through optimization can ensure that the target block can reach the optimal economic benefit during the entire project process.