The invention relates to a polymer microemulsion system for deep profile control of an oil reservoir and a preparation method thereof. The objective of the invention is mainly to overcome the problems that the usage amount of conventional emulsifiers in reversed-phase microemulsion polymerization in the prior art are great and final oil displacement effect is influenced. The polymer microemulsion system for deep profile control of the oil reservoir is prepared through polymerization of reversed-phase microemulsion under the action of a redox composite initiator. The reversed-phase microemulsion comprises, by weight, 50 parts of an oil-soluble solvent, 3 to 20 parts of an emulsifier, 10 to 70 parts of acrylamide monomers, 0.5 to 20 parts of heatproof salt-resistant monomers and 10 to 60 parts of water. With such a technical scheme, the above problems are overcome, and the prepared polymer microemulsion system can be directly diluted with water to obtain an aqueous solution with a desired concentration and be applied to tertiary oil recovery of an oil field.