PURPOSE: To simplify the construction work of cut-off walls by a method in which a water-stop sheet is set in an excavated pit for preceding element, a solidifying agent is placed, a water-stop sheet is also set in an excavated pit for following element, and both elements are connected to each other.

CONSTITUTION: A water-stop sheet 6 having bonding parts 7a on its left and right-handed ends is set with a guide metal 5 in an excavated pit 3 for preceding element, and the ends 6 of the sheet are protected by coupler metals 4. A solidifying agent 20, e.g., concrete, is placed into the pit 3. An excavated pit 13 for following element is then formed, metals 4 are removed, and a water-stop sheet 6 having bonding parts 7b on its left and right-handed ends are hung down into the pit 13 by unwinding the sheet 6. The sheets 6 for preceding elements are connected at the bonding parts 7a and 7b, the guide metal 5 is removed, and the agent 20 is placed into the pit 13 to form a continuous cut-off wall with both elements 6 and 14. The construction work can thus be attained economically without the need for reinforcing bars.