This article was focused on the effects of the NCO/OH molar ratio and 2,2-bis(hydroxyl methyl) propionic acid (DMPA) content during prepolymerization on the physical properties of synthesized waterborne polyurethane (WBPU) by using the polycaprolactone-poly(ethyl glycol)-polycaprolactone triblock copolydiol (PCL-PEG-PCL) as the soft segment. The results showed that the particle size of the WBPUs＇ dispersion decreased with a decreasing NCO/OH molar ratio or increasing DMPA content. Regarding thermal and mechanical properties, the WBPUs had a higher T-g＇s and lower T-m＇s and a higher breaking stress and a lower briefing strain of film with the NCO/OH molar ratio or DMPA content increase. The increasing NCO/OH molar ratio was advantageous to the water vapor permeability (WVP)-breaking stress balance, but the effect of the DMPA content on the WVP was not significant. The WBPU with PCL-PEG-PCL as the soft segment had a smaller particle size dispersion and a better WVP-breaking stress balance than those of WBPU with the blending PCL and PEG as the soft segment.