The work aims to develop alcohol-soluble polyurethane ink with good application prospects, and to explore the influence of the binder synthesized by the molecular weight of the polyurethane monomer on the printability and thixotropy of the ink. Toluene diisocyanate (TDI), polypropylene glycol (PPG, Mn=1000, 1500, 2000, 3000, 4000) and chain extender, 2,2-dimethylolpropionic acid (DMPA) were used as raw materials to synthesize a series of alcohol-soluble polyurethanes (PU1000, PU1500, PU2000, PU3000, PU4000) through chain extension reaction and pre-polymerization. Then, Fourier infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) were adopted to analyze the structure of alcohol-soluble polyurethanes qualitatively. Finally, the influence of polyurethanes, as the binder, synthesized by PPG with different molecular weightson the viscosity, fineness, printability, steady shear viscosity and thixotropy of ink was investigated. The polyurethane binder synthesized by PPG with different molecular weights had an important influence on the properties of ink. With the increase of molecular weight of PPG, the viscosity, fineness and steady shear viscosity of ink firstly increased and then decreased. When Mn=1500, the ink prepared by the synthesized polyurethane had the best comprehensive properties, such as viscosity of 880 MPa∙s, fineness of 5 μm, oil separation rate less than 5%, superior printability (adhesion of 93%, initial dryness of 84 mm/s and gloss of 37) and excellent thixotropy (structure recovery rate of 94.47% at 15 s). The proposed polyurethane will have good application prospect in ink as the binder.