The invention discloses a construction method of a bay window formwork erecting structure formed through one-time pouring, belongs to the technical field of construction formwork erecting, and is used for one-time pouring of an upper structural plate and a lower structural plate of a bay window. The bay window formwork erecting structure comprises a wood formwork I, a vertical wood formwork I, battens, iron wires, a steel frame wood formwork I, a steel formwork, a PC board, an integrated suspended formwork support, truss steel bars, a steel frame wood formwork II, a common suspended formwork support I, a double-batten main keel, a vertical wood formwork II, a batten secondary keel, opposite-pull screws, concrete cushion blocks, supporting steel pipes, a jacking, a steel pipe main keel, a wood formwork II, harness screws, a vertical wood formwork III, a common suspended formwork support II, a line inner side formwork, an outer side formwork, a formwork brace and a steel gasket are in lap joint, and it is guaranteed that an exterior wall bay window modeling joint can be poured and completed at a time along with a main body structure. The bay window plate structure can be formed through one-time pouring along with a main body structure, secondary pouring is avoided, meanwhile, the problem that a suspended formwork support cannot be fixed to a PC plate is solved, and the effects of facilitating site construction and shortening the construction period are achieved.