Abstract: In order to further enhance the water resistance of polyurethane coating agent, waterborne polyurethane modified by fluorinated polysiloxane was synthesized by polyether ( N210 ) and isophorone diisocyanate ( IPDI ) as raw material, hydroxyl terminated fluorinated polysiloxane as modifying agent, dimethylol propionic acid ( DMPA ) as the hydrophilic monomer, and trimethylolpropane ( TMP ) as the chain extender. The effect of the dosage of DMPA, the molecular weight and dosage of modifying agent on the properties of emulsion and its film were discussed, and the modified polyurethane was applied to coat the polyester fabric. The results showed that the stability of the emulsion increased, the particle size of the emulsion decreased, and the hydrophobicity of the film decreased as the dosage of DMPA increased; the stability of the emulsion decreased, the particle size of the emulsion increased, and the hydrophobicity of the film increased as the molecular weight and dosage of modifying agent increased; The performance of waterborne polyurethane achieved the best value when the dosage of DMPA was 5%, the molecular weight of modifying agent was 1694 and its dosage was 6%, the water contact angle of the coated fabric with modified waterborne polyurethane was 138.2°, the hydrostatic pressure of the coated fabric was 644mm. Compared with the unmodified polyurethane, the water resistance of the fabric coated with modified waterborne polyurethane was improved significantly.