Dissolution of CO ₂ in crude oil can change its rheological properties notably, which makes it widely used in the fields of oil displacement, viscosity reduction, transportation and so on. In this study, a pressurized stirring-viscometric equipment was designed based on the stirring viscometry theory, and the corresponding viscometric method was also proposed, so that the viscosity of CO ₂ heavy oil mixture could be determined under the simulation conditions of pipeline transportation. On the basis of this equipment and method, the effects of pressure, shear rate and temperature on the viscosity of CO ₂ heavy oil mixture were probed. It was found that the viscosity of CO ₂ heavy oil mixture decreased exponentially with the increase of pressure. The viscosity of heavy oil system can be greatly reduced by dissolving gas pressure of 2 MPa. Meanwhile, the shear thinning feature became more obvious with increasing pressure of CO ₂. Moreover, the viscosity reducing rate became greater with decreasing temperature at the same pressure. The results of this study provide technical support for the feasibility of transporting viscosity-reduced heavy crude oil by CO ₂.