Ultra-heavy oil resources have gained extensive attention due to their abundant reserves and the shortage of conventional hydrocarbon resources. In this work, we investigate the feasibility of recovering ultra-heavy oil resources using an oil-soluble dissolver, i.e., a type of viscosity reducer, and CO2 assisted steam flooding (DCS flooding) by studying the impact of those agents on oil properties and EOR performance of this approach. Firstly, the effects of steam, CO2, and the oil-soluble dissolver on the oil properties are investigated by comparing the variations in oil viscosity, SARA (saturates, aromatics, resins, and asphaltenes) compositions, asphaltenes structural parameters, and asphaltenes morphology. Then, the feasibility of DCS flooding in improving ultra-heavy oil recovery is investigated by comparing its performance in core flooding experiments with steam flooding and CO2 assisted steam flooding schemes. Next, the sensitivity of various agents in DCS flooding is analyzed by conducting DCS flooding experiments with different amounts and concentrations of those agents. Finally, the chemical components of the produced fluids are analyzed to further understand the dynamic EOR mechanisms of the DCS flooding. The results demonstrate that the oil-soluble dissolver exhibits the best oil viscosity reduction (56.1%) performance through decomposing the asphaltenes of ultra-heavy oil. Meanwhile, DCS flooding presents promising performance in improving ultra-heavy oil recovery (76.78%) compared with steam flooding (59.6%) and CO2 assisted steam flooding (65.26%). Moreover, DCS flooding is also beneficial to decrease maximum steam injection pressure, control the water cut, and improve steam dryness.