The invention relates to the field of crude oil recovery and discloses a polymer with a selective water plugging function as well as a preparation method and application of the polymer. The polymer comprises a structural unit A, a structural unit B and a structural unit C, wherein the structural unit A is a structural unit with a structure shown by a formula (1); the structural unit B is a structural unit with a structure shown by a formula (2); the structural unit C is at least one of a structural unit with a structure shown by a formula (3-1), a structural unit with a structure shown by a formula (3-2) and a structural unit with a structure shown by a formula (3-3). The polymer disclosed by the invention has a high-selectivity water plugging function; by adopting a water plugging material formed by the polymer, an effect of plugging water rather than oil can be obtained with high selectivity. The formula (1), the formula (2), the formula (3-1), the formula (3-2) and the formula (3-3)are shown in the description.