The present invention relates to a polymer expanding material in infiltration or seepage multi-water environment and a preparation method thereof, belonging to a technical field of polymer expanding foam materials. The polymer expanding material includes the following parts of materials by weight: 20-30 parts of rosin polyester polyol, 20-50 parts of isocyanate, 20-40 parts of PhireGuard® MB-512, 5-10 parts of HFO-1233zd, 1-2 parts of surfactant, 0.01-1 part of catalyst, and 0.01 parts of benzoyl chloride. The present invention has high sand fixing body strength, fast curing speed, good elastoplasticity, good pouring property and permeability, and good expanding property, which is suitable for infiltration or seepage multi-water environment, especially for dam infiltration, piping, and other problems during construction and subsequent operation of water conservancy projects.