A polymer grouting method for constructing an ultra-thin anti-seepage wall meeting requirements of anti-seepage designs of dams, includes the following steps of: forming continuous slots on a body of the dam and the foundation which need seepage-proofing and reinforcing; and injecting two-component expansive polymer grouting materials to the slots through grouting pipes, a volume rapidly expands after the polymer grouting materials reacts and the slots are filled to form a polymer ultra-thin body, the polymer ultra-thin bodies which are adjacent are cemented together to form a continuous, uniform, and regular cementing ultra-thin polymer anti-seepage wall; this invention is different from the conventional anti-seepage wall technology whatever through the material, the mechanism or the construction methods, which has the advantages such as speediness, ultra-thinness, minimally invasive, lightness, high toughness, economy, and durability, applied in reinforcement projects of a number of the dams and dikes.