The invention provides an arc-shaped trowel capable of achieving mutual use of internal and external corners and a using method of the arc-shaped trowel, and relates to the technical field of civil engineering. The arc-shaped trowel comprises a first trowelling plate and a second trowelling plate which are connected through an arc-shaped plate to form a V shape, the side, opposite to the second trowelling plate, of the first trowelling plate is provided with a first sliding rail, the first sliding rail extends in the length direction of the first trowelling plate, the side, opposite to the first trowelling plate, of the second trowelling plate is provided with a second sliding rail, the second sliding rail is parallel to the first sliding rail, a first supporting rod and a second supporting rod are arranged between the first trowelling plate and the second trowelling plate, one end of the first supporting rod is slidably connected with the first sliding rail, the other end of the firstsupporting rod is rotatably connected with one end of the second supporting rod through a rotating shaft, the other end of the second supporting rod is slidably connected with the second sliding rail, and a third sliding rail and a fourth sliding rail are formed in the bulged side on the arc-shaped plate. The four corners of the inner and outer edges of a cube of a transformer accident pool can be each turned into a right-angle arc shape, and thus collision damage is reduced.