Abstract: Bohai L oilfield belongs to heavy oil reservoir, which has a problem of low water drive development. In order to improve the difference between oil and water, experiments and mechanism of wetting ability between heavy oil emulsifier and reservoir rock, emulsifying ability between heavy oil emulsifier and crude oil, interfacial tension and viscosity reduction effect were carried out. The results show that emulsifier can transform lipophilic rock into hydrophilic rock, and it can reduce the hydrophilicity of hydrophilic rock, which is beneficial to stripping crude oil from rock surface and improving oil washing efficiency. When the rate of oil and water is lower than "4:6", the emulsifier can be mixed with crude oil to form W/O/W type emulsion, and therefore it can greatly reduce the viscosity of heavy oil and achieve the purpose of improving the fluidity of heavy oil reservoirs and expanding the macroscopic sweep volume. The contact of emulsifier with crude oil in porous media can result in emulsification. The "Jiamin effect" takes place when the emulsion passes through the roar, which results in increased local seepage resistance and enhanced micro-ripple effect.