A method of preparing a reclaimed land bounded by a seawall, the method comprising the following steps: a temporary soil portion construction step of constructing temporary soil portions by piling up soil or stones along the perimeter of a specific area within a planned reclaimed land, setting the planned reclaimed land of the specific area, partitioning the inside of the planned reclaimed land into a plurality of areas and constructing the temporary soil portions along the perimeter of the specific areas; a dredger introduction step of introducing a dredger into an excavation portion within the planned reclaimed land; a banking step of banking earth and sand within the excavation portion in banking portions at a level higher than an inland altitude of the inland waters of the seawall and toward insides of the temporary soil portions using the dredger, by piling up earth and sand into banking portions other than the excavation portions from the planed reclaimed land, so that a ground depression is formed within the excavation portion of the planned reclaimed land that has been generated by dipping up earth and sand and, at the same time, by forming the banking portions higher than the inland waters of the seawall in the remaining portions of the planned reclaimed land; a dredger discharging step of externally discharging the dredger outside of the planned reclaimed land before completing the banking portions; a drainage step of externally draining water within the excavation portion outside of the planned reclaimed land after completing the banking portions within the planned reclaimed land; a drying step of drying the earth and sand within the planned reclaimed land; and an installing step of installing a cut-off wall in a circumference of the excavation portion so that the circumference of the excavation portion formed through the dredging in the excavation portion can be cut off after the drying step in order to prevent water from being introduced into the ground depression formed in the planned reclaimed land. a temporary soil portion construction step of constructing temporary soil portions by piling up soil or stones along the perimeter of a specific area within a planned reclaimed land, setting the planned reclaimed land of the specific area, partitioning the inside of the planned reclaimed land into a plurality of areas and constructing the temporary soil portions along the perimeter of the specific areas; a dredger introduction step of introducing a dredger into an excavation portion within the planned reclaimed land; a banking step of banking earth and sand within the excavation portion in banking portions at a level higher than an inland altitude of the inland waters of the seawall and toward insides of the temporary soil portions using the dredger, by piling up earth and sand into banking portions other than the excavation portions from the planed reclaimed land, so that a ground depression is formed within the excavation portion of the planned reclaimed land that has been generated by dipping up earth and sand and, at the same time, by forming the banking portions higher than the inland waters of the seawall in the remaining portions of the planned reclaimed land; a dredger discharging step of externally discharging the dredger outside of the planned reclaimed land before completing the banking portions; a drainage step of externally draining water within the excavation portion outside of the planned reclaimed land after completing the banking portions within the planned reclaimed land; a drying step of drying the earth and sand within the planned reclaimed land; and an installing step of installing a cut-off wall in a circumference of the excavation portion so that the circumference of the excavation portion formed through the dredging in the excavation portion can be cut off after the drying step in order to prevent water from being introduced into the ground depression formed in the planned reclaimed land.