Waterborne polyurethane emulsions with sulfonic group were synthesized by a prepolymer process using dimethylol propionic acid (DMPA) and self-prepared sulfonic hydrophilic monomer (namely 1 2-dihydroxy-3-propanesulfonic acid salt DHPA). The structure of the films was confirmed by means of FTIR. The test results indicated that the DHPA has been synthesized and introduced into the chain of polyurethane. The results indicated that the average particles diameter of polyurethane emulsions became smaller and particles distribution width became narrower, with the increase of the weight of DHPA. TEM photos show that PU emulsions were well-dispersed with neat appearance. The viscosity of emulsions decreased, with the increase of shear rate, showing pseudo-plastic characteristics.