On the basis of analysis of the main reasons for poor oil recovery of heavy oil reservoir by water flooding and according to the mechanism of the enhancing oil recovery, a chemical agent, which is composed of nonionic surfactants, anionic surfactants and emulsion stabilizers, can adapt to heavy oil reservoir with high temperature and high salinity. The core displacement experiments show that displacement system containing chemical agent can enhance oil recovery by over 20% comparing to water flooding, and the chemical agent contained in produced fluid has no negative effect on demulsification. Mechanism by which chemical agent enhance oil recovery of heavy oil reservoir are: (1) significantly decreasing viscosity of heavy oil to improve mobility ratio volumetric and improve sweep efficiency; (2) decreasing oil-water interfacial tension to increase capillary number and improve oil displacement efficiency; (3) changing wettability of the rock surface from oil-wet to water-wet to change capillary force from the resistance force to the motive force, and drive the residual oil out of the small pores and the wall of pores and increase oil displacement efficiency.

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