A ring-shaped cofferdam and temporary pit excavation structure using tapered square pipes (210, 220), the structure comprising a plurality of tapered square pipes (210, 220) with a trapezoidal cross-section, wherein each of the plurality of tapered square pipes has a coupling protrusion (211, 221) or a coupling groove (212, 222) formed in a longitudinal direction on a first side, and wherein each of the plurality of tapered square pipes has a coupling protrusion (211, 221) or a coupling groove (212, 222) formed in the longitudinal direction on a second side, wherein the plurality of tapered square pipes (210, 220) are assembled by coupling the coupling protrusions (211, 221) and the coupling grooves (212, 222), and wherein a long side of two parallel sides of the trapezoid is disposed outside, and a short side is disposed inside, characterized in that tapered cross-sections of some of the plurality of tapered square pipes (210, 220) are inclined at different angles, and wherein the ring-shaped cofferdam and temporary pit excavation structure further comprises an anchor member that is fitted in a lower end of one of the plurality of tapered square pipes (210, 220), wherein the anchor member has: a fitting portion formed at an upper end of the anchor member to be fitted in a lower end of one of the plurality of tapered square pipes; and an anchor portion extending uniformly a predetermined length from the fitting portion and then decreasing in cross-sectional area toward a lower end, and an upper end of the anchor portion is larger in cross-sectional area than the fitting portion. wherein each of the plurality of tapered square pipes has a coupling protrusion (211, 221) or a coupling groove (212, 222) formed in a longitudinal direction on a first side, and wherein each of the plurality of tapered square pipes has a coupling protrusion (211, 221) or a coupling groove (212, 222) formed in the longitudinal direction on a second side, wherein the plurality of tapered square pipes (210, 220) are assembled by coupling the coupling protrusions (211, 221) and the coupling grooves (212, 222), and wherein a long side of two parallel sides of the trapezoid is disposed outside, and a short side is disposed inside, characterized in that tapered cross-sections of some of the plurality of tapered square pipes (210, 220) are inclined at different angles, and wherein the ring-shaped cofferdam and temporary pit excavation structure further comprises an anchor member that is fitted in a lower end of one of the plurality of tapered square pipes (210, 220), wherein the anchor member has: a fitting portion formed at an upper end of the anchor member to be fitted in a lower end of one of the plurality of tapered square pipes; and an anchor portion extending uniformly a predetermined length from the fitting portion and then decreasing in cross-sectional area toward a lower end, and an upper end of the anchor portion is larger in cross-sectional area than the fitting portion. a fitting portion formed at an upper end of the anchor member to be fitted in a lower end of one of the plurality of tapered square pipes; and an anchor portion extending uniformly a predetermined length from the fitting portion and then decreasing in cross-sectional area toward a lower end, and an upper end of the anchor portion is larger in cross-sectional area than the fitting portion.