The invention discloses a method for evaluating sealing properties of cap rocks in carbon dioxide flooding storage, and belongs to the field of a carbon dioxide flooding process. The method is characterized by comprising the following steps of 1) building a carbon dioxide geological storage body well log response model; 2) determining a regional cap rock, a direct cap rock and an interlayer in a reservoir; 3) compiling a cap rock plane distribution chart, and determining cap rock player plane distribution feature parameters; 4) calculating a seepage velocity of carbon dioxide of each phase state in the cap rocks, and establishing percolation comprehensive evaluation parameters; 5) building a porosity and displacement pressure fitting model and a permeability and throat feature parameter fitting model; 6) performing numerical simulation on a reaction process of different chemical substances in the cap rocks, and determining erosion resistance of different cap rocks; and 7) establishing evaluation indexes for the seal properties of the cap rocks in the carbon dioxide flooding storage of an oil field, thereby performing comprehensive evaluation on the sealing abilities of the cap rocks. According to the method, multi-factor stereoscopic comprehensive evaluation is performed for the cap rocks, so that the precision of evaluating the sealing abilities of the cap rocks is greatly improved.