The invention relates to pH sensitive regenerated polymers I and II. In the polymer I, the viscosityaverage molecular weight is 2.93*10<6>g / mol, the isoelectric point is 2.87, the recovery rate is 98.87 percent, the polymer I is randomly copolymerized by compounds shown in formulae (1), (2) and (3), and the molar ratio of feeding is 23:2:1. In the polymer II, the viscosityaverage molecular weight is 3.37*10<5>g / mol, the isoelectric point is 3.91, the recovery rate is 97.18 percent, the polymer I is randomly copolymerized by compounds shown in formulae (1), (2), (3) and (4), and the molar ratio of feeding is 23: 8: 1: 6. The invention also relates to a related preparation method, an aqueous two-phase system formed by the pH sensitive regenerated polymers, as well as an application of the aqueous two-phase system. The two types of polymers are pH sensitive and reversely soluble, the formed regenerated aqueous two-phase system is pH sensitive, and twenty percent of the two types of phase-forming polymers can be efficiently retrieved, so that the use cost is greatly reduced, the retrieving is simple and convenient, and the pH sensitive regenerated polymers provided by the invention is suitable for large-scale popularization and application.