Abstract: In polymer flooding in offshore oil fields, the existing polymer cannot meet the requirements of online flooding fluid formulation on offshore platforms due to its low viscosity and poor solubility in seawater. A new type of zwitterionic copolymer (AM/DEPS) was synthesized through inverse emulsion polymerization with acrylamide (AM) and methyl acryl oyloxyethyl-N,N-diethyl-CHAPSO(DEPS) as the comonomer. The structure of the copolymer was analyzed by IR and HNMR spectrum. Analysis results showed that the copolymer molecular chain contains acrylamide, DEPS links and the DEPS zwitterionic monomer is introduced into the molecular chain of the copolymer. The effects of monomer DEPS mole fraction, emulsifiers, initiator and the reaction temperature on the intrinsic viscosity of the copolymer were analyzed. The optimum copolymerization reaction condition were determined: reaction temperature around 25-30℃, initiator percentage 0.08%, emulsifier to oil phase mass ratio 1∶8 and DEPS monomer mole fraction 2.5%. The salt thickening and solubility of the copolymer were evaluated and it showed that the copolymer emulsion could be quickly dissolved in seawater with excellent viscosifying effect, which could meet the requirement of flooding fluid online formulation with seawater for offshore platforms.