The invention discloses an acrylamide copolymer, and a preparation method and an application thereof. The acrylamide copolymer contains a constitutional unit A, a constitutional unit B, a constitutional unit C and a constitutional unit D, wherein the constitutional unit A is a constitutional unit represented by formula (1) and/or a constitutional unit represented by formula (2), the constitutional unit B is one or more of constitutional units represented by formula (3), formula (4), formula (5) and formula (6) respectively, the constitutional unit C is a constitutional unit represented by formula (7) and/or a constitutional unit represented by formula (8), and the constitutional unit D is a constitutional unit represented by formula (9) and/or a constitutional unit represented by formula (10); and the viscosity average molecular weight of the acrylamide copolymer is 2,000,000-25,000,000. The acrylamide copolymer has the advantages of high drag reduction rate, high heat and salt resistance, good high-shear resistance, good water solubility, good compatibleness with clay inhibitors (alcohol), and small damages to the stratum.