This paper introduced a new zwitter-ion terpolymer through aqueous solution polymerization, which can be used in the drilling fluids. The monomers are acrylamide(AM),diallyl dimethyl ammonium chloride(DMDAAC) and sodium p-styrenesulfonate (SSS). A series of experimental factors were also discussed and the optimum scheme of copolymerization was obtained，that is，monomer mass is 25% ，temperature of reaction is 60℃ ，dosage of initiator is 0.5% ，molar ratio of monomer n(AM)∶n(DMDAAC)∶ n(SSS) is 8∶1∶1，reaction temperature is 60℃．The results of infrared characterization have confirmed that the structure of the product in question is consistent with the original design. The results showed that the product could control the fluid loss well and API could reach 7mL, otherwise it had inhibitory effect, which were worth popularization.