The invention provides a film-forming polymer emulsifier and a preparation method thereof. The polymer emulsifier is prepared from the following components in parts by weight: 20-50 parts of EO segment-containing copolymers, 10-40 parts of diisocyanate, 1-50 parts of an environment-friendly solvent, 2-10 parts of DMPA (dimethylol propionic acid) and DMBA (bis(hydroxymethyl)butyric acid), 2-10 parts of a chain extender and 2-10 parts of TEA(triethanolamine), 0.1-3 parts of a bismuth catalyst and 0.1-3 parts of an antioxidant I-1010, wherein the EO segment-containing copolymers contain PEG/PTMGcopolymers and other polyalcohols such as polyester and polycaprolactone, besides PEG/PPG copolymers, and are film-forming substances and can form films, after the substances are added to oily resin,oily resin can be emulsified in water, most of properties of the oily resin can be maintained when the substances are used for emulsifying common finished oil resin, and the oily product is directly hydrated. The process of hydrating the oily product can be greatly simplified, and original properties of the oily product is greatly retained.