Abstract: A series of cationic water-borne polyurethane(CWPU) was synthesized from isophorone diisocyanate (IPDI), polyneopentanediol adipate (P756) and hydrophilic N-methyl dihydroxyethyl amine (N-MDEA) by using the one-step process. Phase inversion of the cationic water-borne polyurethane was established by tracing the change of conductivity and speed of stirrer during the dispersion process.The conductivity of CWPU increased to a maximum, and then decreased to a stabe value.This result showed that the enrichment of partial anion and the gemination of ion occurred successively during the process of phase inversion.Conductivity kept stable after the Stern layer of the CWPU colloid particles were formed. The effects of dispersion temperature and the amount of N-MDEA on the particle size of CWPU were discussed. The particle size and polydispersity of CWPU were decreased with higher dispersion temperature and increasing amount of hydrophilic chain-extender. There existed optimal dispersion temperature and amount of chain-extender of the cationic polyurethane during the dispersion process. The DSC and DMA data of the cast film of CWPU showed that water could enter the partially disrupted ordered structure of the CWPU hard segment when phase inversion occurred at an appropriate temperature, and the stable, smaller particle size and polydisperse of the CWPU could be obtained.