To provide an underground intercepting-plate construction method in which high impervious performance is maintained stably even when there is the defective filling of a sealing material or even when external force such as vibrations is applied while an intercepting plate is driven easily and workability is improved.

The underground intercepting-plate construction method is composed of the first process, in which a pit is formed into a ground in specified depth and a low-strength impervious wall 5 having unconfined compressive strength of 0.1-1.0 kgf/cm2 is constructed in the pit 4, and the second process in which an intercepting plate 10 is driven into the low-strength impervious wall 5 and an impervious wall 20 having sandwich structure in which the low- strength impervious wall 5 pinches the intercepting plate 10 from both surfaces and an underside is built.