The invention relates to a temperature and salt-resistant AM / ACD / AE copolymer used as an oil displacement agent in the petroleum exploitation and a preparation method thereof. The temperature and salt-resistant AM / ACD / AE copolymer can meet the requirements of the injected liquid viscosity with the incessant increasing of the oil reservoir temperature and the stratum mineralization. The technical scheme of the invention is characterized in that the mole ratio of the raw materials used in the preparation of the copolymer comprises, by mole percentage, 88.2-91.4% of an AM monomer, 8-11% of an ACD monomer, 0.6-0.8% of an AE monomer, an oxidizing agent potassium persulphate which accounts for 0.3-0.5% of the total weight of the monomers, and a reducing agent sodium bisulfite which accounts for0.35-0.45% of the total weight of the monomers. The preparation method provided by the invention comprises the following steps of: adding AM, ACD and AE into a container, adding water to produce a solution at the concentration of 15%, dissolving with stirring, adding the oxidizing agent and the reducing agent with uniformly blending, deoxygenizing by filling nitrogen, reacting at the temperature of 40-50 DEG C for 4-5 hours, washing and drying to obtain the AM / ACD / AE copolymer. The preparation method provided by the invention is simple and feasible with mild reaction conditions; the product prepared by the method has inclusion and aggregation functions as well as temperature and salt-resistant performance, and can be used in tertiary oil extraction.