To efficiently construct a water stopping structural body capable of sufficiently ensuring cut-off efficiency and strength as well as the excellence in flexibility and auto-repairability.

High expansive slurry mixing bentonite with ethanol and high water absorbing resin is used for a ground water stopping material, and the ground water stopping material is injected in the ground to agitatedly mix in situ to form the water stopping structural body by swelling high water absorbing resin through the substitution of ethanol in the ground water stopping material for the ground water. High expansive sand mixture mixing the high expansive slurry further with sandy soil is used for the ground water stopping material, and the ground water stopping material is only filled in a hollow section in the ground to form the water stopping structural body. As mix proportion of the high expansive slurry, ethanol of 60 to 150 pts.mass. and high water absorbing resin of 5 to 50 pts.mass to bentonite of 100 pts.mass are desirable. The high expansive sand mixture is preferably formed by mixing the sandy soil of not more than 30 times of mass of bentonite with the high expansive slurry.