In this study, a novel pH-sensitive and reversible water-soluble polymer(PABC) forming aqueous two-phase systems(ATPS) was synthesized by using 2-(dimethylamino) ethyl methacrylate, t-butyl methacrylate, and methyl methacrylate as monomers and 2,2'-azo-bis-isobutyronitrile as initiator. The PABC could be recovered by adjusting isoelectric point (PI) to 8.4, and recovery at PI could reach 95%. ATPS was formed by 5% (w/w) PABC and 10% (w/w) PEG20000. The partition coefficient K of lysozyme was 6.8, and the partition coefficient K of bovine serum albumin could reach 12.5 in the ATPS.