Binary composite system 1# has a non-ultralow oil-water interfacial tension（10-1 mN/m level），good emulsion stability，and strong viscosity reduction capacity by emulsification. In order to investigate the displacement efficiency of this system on conventional heavy oil，evaluations are carried out on five aspects including：interfacial tension，degree of emulsification difficulty，emulsion stability，viscosity reduction capacity by emulsification，and displacement efficiency. The results are compared with binary composite systems 2# and 3# with ultra-low interfacial tension（10-3 mN/m level）as well.The results show that the emulsion formed by 1# is more stable，indicating that there is no correlation between emulsion stability and ultra-low interfacial tension，though 1# is more difficult to emulsify heavy oil than 2# and 3#. Percolation experiment results show that 1# could significantly decrease the flowing resistance of heavy oil，while 2# and 3# have no similar effect. According to the emulsifying difference of systems 1#，2# and 3#，it is believed that the emulsion stability is the key to improve the flow of heavy oil through emulsification. The oil displacement test result show that composite system 1# could increase oil recovery by 15.6%，which is much higher than that of 2# and 3# with ultra-low interfacial tension（about 10.0%）. This indicates that emulsion stability and viscosity reduction capacity by emulsification are important to the displacement of conventional heavy oil in binary composite system.