Abstract: In order to reveal the relationship between sizing performance and molecular structure of water-soluble polyurethane used as warp sizing agents, a series of water-soluble polyurethane were synthesized using 2,4-toluene diisocyanate, polypropylene glycol, dimethylol propionic acid and 1,4-butanediol as monomers. The structure was characterized by 1H NMR. Through varying the molar contents of the 2,4-toluene diisocyanate, polypropylene glycol, dimethylol propionic acid and 1,4-butanediol, the solubility, adhesion-to-fibers, and film behaviors of the polyurethane were investigated for determining its reasonable structure. The results demonstrate that the solubility of the polyurethane was enhanced with the increase in the content of dimethylol propionic acid. The adhesion and film strength increase with the decrease in molar content of polypropylene glycol. However, the decrease gradually damaged abrasion resistance of sizing film. Based on the performances considered, the polyurethane with better performances could be prepared by adopting a monomer formulation in which the proportion of 2,4-toluene diisocyanate, polypropylene glycol, dimethylol propionic acid and 1,4-butanediol were 1.05/0.3/0.3/0.4.