In order to clarify the relative importance of ultra-low interfacial tension（IFT）and emulsification mechanisms for recovering heavy oil by compound flooding，the IFT，emulsification，foam and oil displacement performances of two compound systems guided by ultra-low IFT and good emulsification were studied. The results showed that，for the ultra-low IFT system，the oil-water IFT could be reduced to 2.6×10-4 mN/m，but it performed poorer in foaming and stabilizing emulsion and foam than the emulsified compound system，while the oil-water IFT of the later was only 0.25 mN/m. Although the properties of those two systems differed greatly，the increased oil recovery by ultra-low IFT system was similar to that of emulsion system during the simple compound flooding，which might be caused by the poor sweep volume during flooding. However，that increased by ultra-low IFT foam was 38.3%，which was much higher than that of 28.9% by emulsion foam flooding. This indicated that the mechanism of oil washing by ultra-low IFT was more critical than that of viscosity reduction by oil-in-water emulsification during foam flooding. Ultra-low IFT foam flooding （water alternative gas injection） could improve heavy oil recovery more than increasing the slug of compound system. The recovery could be increased to 38.3% by 0.3 PV the former strategy，while 30.7% by 0.5 PV the latter. Ultra-low IFT foam flooding was the better way to improve heavy oil recovery at the present，and the displacement of heavy oil by single compound system might be a waste of chemical agents.