To address the challenges of high difficulty in achieving miscibility and low recovery rate in CO2 flooding of shale oil, a technology of DME-assisted CO2 flooding to enhance shale oil recovery rate was proposed. Based on the understanding of the effects of DME on the interfacial tension, viscosity and miscibility pressure between CO2 and crude oil, three types of shale with different pore structures from the Huahai Depression in the Jiuquan Basin were selected to conduct core experiments of CO2 flooding and DME-assisted CO2 flooding. Low-field core nuclear magnetic resonance testing technology was used to study the oil displacement characteristics of CO2 flooding and DME + CO2 flooding in shales with different pore structures, quantitatively characterize the degree of crude oil mobilization in microscopic pores, and evaluate the potential of DME + CO2 flooding to enhance shale oil recovery rate. The experimental results show that the pore structures of the target reservoir shales can be classified into types I, II and III, with the pore structures and seepage capabilities getting worse in sequence and the proportion of nano-pores increasing. DME significantly reduces the viscosity, interfacial tension and miscibility pressure of crude oil by increasing the solubility of CO2 in crude oil, with the optimal DME content being 15%. Compared with CO2 flooding, DME + CO2 flooding can significantly increase the recovery degree of small and large pores in the three types of shales. With the increase of injection pressure, DME + CO2 can achieve miscibility at a lower injection pressure, further significantly increasing the recovery degree of small pores, and the contribution of small pores to the recovery rate increases. Among them, the recovery rate increase of types II and III shales is greater than that of type I. The recovery rates of CO2 flooding for the three types of shales from high to low are II, I and III, while the recovery rates of DME + CO2 flooding from high to low are II, III and I. This indicates that DME + CO2 flooding not only significantly increases the recovery rate but also stimulates the development potential of type III shales with poor pore structures. The research results provide a new method for enhancing the development of shale oil through CO2 injection.