Rheological behavior and thermostability of aqueous solution of carboxymethyl hydroxy-propyl cellulose ether(CMHPC) in the temperature range from 25 to 80℃ were studied by rotatory viscometer. The energy of ac'ivation of viscous flow

related with Arrhenius equation is between those of HEC and PAC. The research results showed that CMHPC was similar to PAC at higher CM content and corresponded to Ostwad-Der Waele model perfectly. A higher HP content the flow curve didn't follow the model. After adding small molecule electro-lytes into CMHPC aqueous solution COO-ions were shielded by counter ions. Thus the hydro-xypropyl group became major effect and influenced the rheological behavior.The salt tole-rance of CMHPC in solutions was also studied with different type of ions and concentration.