1,3,5-triacryloylhexahydro-1,3,5-triazine(TAT) and mercaptoethanol were used to synthesize a kind of sulfur-containing trifunctional crosslinker S-TAT which will participate in a reaction of polyurethane system with trimethylolpropane (TMP) together. The purpose was to get waterborne polyurethane. The structure, thermal properties and mechanical properties of the aqueous polyurethane films were characterized by attenuated total reflection infrared (ATR-FTIR), thermogravimetric analysis, X-ray diffraction and electronic tensile machines. The effects of S-TAT content on the properties of polyurethane influences. The results showed that the crystallinity of the film and the glass transition temperature of the soft segment increase and then decrease,the suction rate of the film in water decreased first and then increased.The tensile strength, elongation at break and elastic modulus increase with the content of S-TAT to TMP ratio. When n(S-TAT):n(TMP)=3:2, the crystallinity of the film WPU4 was 24.91%, the glass transition temperature of the soft segment was -36.36℃, the water absorption in the water reduced to 7.34%; When n(S-TAT):n(TMP)=5:0, the tensile strength of the film WPU6 was 19.8 MPa, the elongation at break of 399%, and the elasticity modulus increased to 39.8MPa.