The chemical combination flooding is one of the key techniques for enhanced heavy oil recovery. More importance is attached to the emulsification and viscosity reduction mechanism during the development of such combination systems，and some efficient emulsification systems are formed. The“oil recovery increment”caused by strong emulsification，however，is still unclear，which results in difficulties in determining the actual contributions of emulsification to oil displacement.In this study，three combination systems with significantly different properties were collected，namely，the ultralow interfacial tension system（#1），the strong emulsification system（#2），and the system with both ultra-low interfacial tension and strong emulsification（also called dual-effect system）（#3）. The comparative studies of interfacial tension，emulsification performance，and oil displacement at different water-oil viscosity ratios were carried out. The results reveal that the second and third systems（#2 and #3）are more capable of stabilizing heavy oil emulsions than the ultra-low interfacial tension system（#1），and the contributions of emulsification to the combination flooding in heavy oil reservoirs varies with the water-oil viscosity ratios. When the water-oil viscosity ratio is less than 0.200，the oil recovery of the dual-effect system（#3）is 3.6%-6.7% higher than that of the ultra-low interfacial tension system（#1），which indicates that emulsification can enhance the oil displacement capacity of the system. When the ratio is equal to or greater than 0.200，however，the oil displacement effect of the three systems is similar，and the impact of emulsification is significantly reduced or can even be ignored. The foam combination flooding could significantly raise the oil recovery increment in comparison with the binary combination flooding，and more importantly，it can reduce the water-oil viscosity ratio limits required by combination system emulsification performance for heavy oil displacement from 0.200 to 0.150. It can be seen that the performance of combination systems of combination flooding in heavy oil reservoirs should be determined according to the difference in water-oil viscosity ratios.