Affected by reservoir conditions such as high formation pressure，thin thickness reservoir and active edge or bottom water，some heavy oil reservoirs suffer from large heat loss，high cost and low recovery during thermal recovery. Therefore，effective development is difficult. Through indoor flooding experiments，the enhanced oil recovery mechanism of viscosity reducer flooding，polymer flooding and chemical viscosity-reducing compound flooding in the heavy oil reservoir was studied，and the effect of different flooding systems on the enhanced oil recovery of heavy oil was compared and analyzed.The results show that the chemical viscosity-reducing compound flooding system that contains water-solubility viscosity reducer and polymer can increase the recovery efficiency by 16.04%，which is superior to the flooding using the viscosity reducer or the polymer system alone. From the viewpoint of oil change efficiency，the polymer concentration in the slug of compound flooding was optimized to be 0.3%，and the water-solubility viscosity-reducer concentration was optimized to be 1.0%；from the view point of improving the recovery efficiency，the injection pattern of the viscosity reducer post-slug and the polymer pre-slug is optimized and the recovery efficiency can be increase by 7.2% to 10.7%. On this basis，the optimal volume ratio of water-solubility viscosity reducer to polymer slug is 3∶2. In the heterogeneous model and the microscopic visualization model，the chemical viscosity-reducing compound flooding not only has the oil-displacement mechanism of both the viscosity-reducing agent and the polymer，but also produces a synergistic effect，which can greatly improve the sweep range and oil washing efficiency of heavy oil compared with chemical flooding by a single agent.