TDI as main isocyanate, IPDI as end-capping reagent, waterborne polyurethane emulsions (WPUs) surface-sizing agent have been obtained. The properties of WPUs and papers sized by WPUs with different DMPA content, different NCO/OH molar ratio and nNCOTDI/nNCOIPDI are systematically examined. The results show that WPUs are new kinds of surface sizing agents with good properties. The water resistance, surface gloss and smoothness of papers sized by WPUs have dramatically increased. The folding endurance, tearing resistance and tensile strength of WPU sized papers are observed to increase obviously.