Waterborne polyurethanes(WPUs) based on isophorone diisocyanate(IPDI), Polybutylene adipate (PBA) and dimethylolproprionic acid(DMPA) were synthesized by prepolymer mixing process. Effect of NCO/OH ratio on the properties of the dispersions was studied. The structure of the WPUs was studied by FT-IR. Besides the mechanical properties and water swelling of the films, the number average diameters of the dispersions and the viscosity of WPUs were characterized, results showed that all WPUs had higher solid content (over 45%). With higher NCO/OH ratio, WPUs had bigger dispersion size and lower dispersion viscosity; the casting film had higher water swelling, lower tensile strength, and more water-soluble substance.