To figure out the influence of different factors on the diffusion of carbon dioxide (CO2) in oil-saturated porous media, an experimental method using a multifunctional core displacement instrument instead of a PVT Cell was proposed to monitor the pressure decay in ten cores (porous media) under high temperature from 20 to 80 degrees C and pressure from 15 to 30 MPa. Then, the traditional diffusion model and the improved diffusion model in this work without and with consideration of the influence of tortuosity were applied to calculate the diffusivity of CO2, respectively. Also, it can be found that the novel diffusion model can predict the pressure decay and the diffusivity of CO2 in porous media well, indicating that the proposed model in this work can be used as an effective method to predict the diffusion coefficient of CO2 in porous media. Additionally, the influences of tortuosity, temperature, and initial pressure on the diffusivity of CO2 in oil-saturated porous media were analyzed. The results showed that the tortuosity of porous media brings to a dramatic decrease of the diffusion coefficient, and the increasing temperature and higher initial pressure benefit the diffusion of CO2 in porous media.