A series of anionic waterborne polyurethane emulsion were successfully synthesized by reacting polycaprolactone diols(PCL),isophorone diamine(IPDI),diethylenetriamine(DETA) and dimethylolpropionic acid(DMPA).The factors affecting its synthetic condition were discussed,and the synthetic process was optimized.The results show that the emulsion owns excellent sizing property when n(NCO)/n(OH) is 1.6,w(DMPA) is 3.4%,w(DETA) is 0.5%,and with 1.0% polymer emulsion addition.The papers’ sizing value can reach 74s,and wet strength approaches 36.02%,folding endurance 125 times.Finally,the polymer was characterized with Fourier transform infrared spectra(FT-IR),thermogravimetry(TG) and scanning electron microscope(SEM).FT-IR indicates that the polymer forms polyurea structure with the DETA addition.TGA indicates that the crosslink of DETA with polyurethane has thermal stability of the modified polyurethanes.SEM indicates that the crosslink of DETA with polyurethane makes the interfaces between surface fiber became blurred,makes paper surface fiber combination closer.