To provide a construction method of an artificial low water permeable layer adopted as a kind of underground water level lowering construction method at underground work of the large depth in the sand ground or the gravel ground having a high underground water level.

A water filling well 3A is arranged in one of the construction object ground, and a pumping well 3B is arranged in the other. At least two aqueous solutions X and Y are simultaneously or separately injected into the ground from the water filling well. Water is pumped up from the pumping well, and a hydraulic gradient is formed in the ground, and an underground water flow is generated to promote permeation. Water permeability of the ground is reduced by generating a fine and water insoluble deposit in the ground by contacting and reacting the two aqueous solutions in the ground.