In this work, pH/thermo dual responsive tertiary amine starch ether was prepared using N,N-di-n-propyl/butyl-2,3-epoxylpropylamind as tertiary ammoniation reagent. Influences of the reaction conditions to the molecular degree of substitution of the product (MS) were investigated, which including reaction temperature, reaction time, quantity of solvent and catalyst NaOH. As the ratio of AGU to tertiary ammoniation reagent was 1:1, MS could be 0.59, under the optimum condition, at that time, the reaction condition was temperature 90oC, n(NaOH):n(AGU)=0.5, m(H2O):m(AGU)=4, reaction time12h. The result of transmittance of the aqueous solution on different pH showed that this kind of tertiary amine starch has excellent pH/thermo dual responsive property. The cloud points(TC) decreased with the increasing of pH or the length of the carbon chains of alkyl group, which could be adjusted critically in the range of 14.9-77.7oC.