Series of internal crosslinking waterborne polyurethanes were prepared from isophorone diisocyanate (IPDI), propylene carbonate polyols (PPC), dimethylol propionic acid (DMPA) as hydrophilic chain extender and trimethylolpropane (TMP) as crosslinking agent. The structure and properties of the polyurethane were characterized by Fourier transform infrared spectrometer ( FT-IR), thermogravimetric analysis ( TGA) , and its water resistance and contact angle were measured. It is found that, with increase of the TMP amount, the thermal property of the WPU film increases. Meanwhile, the water resistance property and the water repellency of the film are also improved.