Shale oil is enriched in DQGL area, and CO2 assisted fracturing of horizontal wells is the main development mode in DQGL area. The fracturing process is carried out in five steps: injection of pre-fluid, CO2, sand carrying fluid, well soak and production. At present, the reservoir factors and process parameters affecting CO2 assisted fracturing oil production have not been thoroughly studied, and its mechanism and suitable conditions are still not clear. In this paper, the numerical simulation technology is applied to establish a three-dimensional isothermal fracturing reservoir model of oil, gas and water three-phase, two porosity and two permeability reservoirs, study the sensitive law of CO2 assisted fracturing stimulation mechanism, and identify the sensitive factors of CO2 stimulation reservoirs and injection parameters. The research results show that the main reservoir factor affecting CO2 oil increase is crude oil viscosity, followed by oil–gas ratio. The crude oil viscosity of the reservoir is directly proportional to the CO2 oil change rate, and the crude oil viscosity is 4 mPa.s or more, the oil–gas ratio has a great influence on the CO2 oil change rate, and the oil change rate is higher at low oil–gas ratio. The process parameters that affect CO2 assisted fracturing oil increase are mainly CO2 consumption and soak time. Under the condition of low gas oil ratio, the CO2 consumption increases and the oil change rate increases. However, with the increase of gas oil ratio in the reservoir, the oil change rate decreases. The reason is that CO2 oil increase and viscosity reduction is partially replaced by dissolved gas. The simulation results of different gas oil ratio and soaking time after fracturing show that the oil change rate is higher after soaking time for 30 days.