The invention relates to a temperature and salt resistant copolymer KWKY-PAD for oil field and a preparation method thereof, and mainly solves the problem that polyacrylamide is easy to hydrolyze at high temperature and high salinity in the prior art. The temperature and salt resistant copolymer KWKY-PAD as shown in formula (I) is obtained by the copolymerization of acrylamide and a N-alkyl substituted acrylamide derivative. The technical scheme provided by the invention greatly solves the problem. By the adoption of the preparation method, the hydrolytic stability of the copolymer is raised,and the copolymer has good viscosifying ability and hydrolytic stability at high temperature and high salinity as well as good temperature and salt resistance. The copolymer provided by the inventioncan be used in an oil displacement agent for oil extraction in oil field, and also can be used in oil field application fields of a thickening agent of fracturing fluids, a water plugging profile modification agent, a drilling fluid processing agent and the like. In addition, the preparation method requires less monomer, is simple and is suitable for industrialization.