The invention relates to a polymer expanding material used in a permeation or seepage waterish environment and a preparation process of the polymer expanding material and belongs to the technical field of polymer expanding foam materials. The material is prepared from raw materials in parts by weight as follows: 20-30 parts of rosin polyester polyol, 20-50 parts of isocyanate, 20-40 parts of PhireGuard MB-512, 5-10 parts of 1,1-dichloro-1-fluoroethane, 1-2 parts of a surfactant, 0.01-1 part of a catalyst and 0.01 parts of benzoyl chloride. The material has high sand stabilization strength, high curing speed, good elastoplasticity, good pouring property, permeability and expansibility, is applicable to the permeation or seepage waterish environment, particularly to construction of water conservancy projects and following operation processes and is used for solving problems of dam permeation, piping and the like.