ABA triblock copolymer [A＝2-(diethylamino)ethylmethacrylate], DEAEMA|B＝2-methacryloyloxyethyl phosphorylcholine, MPC] (PDEAEMA-b-PMPC-b-PDEAEMA) was synthesized via atom transfer radical polymerization (ATRP) in methanol using CuBr/2,2-bipyridyl as the catalyst system and diethyl-meso-2,5-dibromoadipate as the initiator. PDEAEMA-b-PMPC-b-PDEAEMA was characterized by ¹H NMR and GPC. The pH sensitivity of the triblock copolymer aqueous solutions was investigated by transmittance and viscosity measurements. The micellization of the triblock copolymer aqueous solutions was investigated by surface tension measurements, fluorescence probe and transmission electron microscope. The results show that the resultant block copolymer has pH sensitivity, the critical phase change pH was 7～7.5, “flower micelle” can be formed through adjusting solution pH, and the critical micelle concentration (CMC) of the triblock copolymer aqueous solution was measured.