The effect of water flooding development in low permeability reservoir is generally poor, and CO2 flooding can effectively improve the degree of crude oil recovery. In order to analyze various factors affecting the effect of CO2-assisted gravity flooding, based on the research mechanism of gas-injection-assisted gravity flooding, a mechanism model of one injection and one production was established to analyze the influence law of geological factors and development factors, and the orthogonal experimental design method and Shapley value method were used for multi-factor analysis. The results show that the positive rhythm reservoir is more suitable for CO2-assisted gravity flooding. Reservoir dip Angle, average permeability and gas injection velocity are positively correlated with development effect. The ratio of vertical permeability to horizontal permeability and the difference of permeability stage were negatively correlated with the development effect. If the ratio of gas injection and dimensionless horizontal well section length is set to 0.8, the CO2-assisted gravity flooding effect can be effectively improved. The ratio of vertical permeability to horizontal permeability has the highest influence on CO2-assisted gravity flooding. The research results provide technical guidance and theoretical support for improving the development effect of CO2-assisted gravity flooding in low permeability reservoirs.