The invention discloses a reinforcement device of a stiff cylinder and shear wall composite structure formwork. The reinforcement device of the stiff cylinder and shear wall composite structure formwork comprises a fixing screw rod, welding sleeves, fixing screws and a steel bar hoop, wherein the welding sleeves are respectively welded to two ends of the steel bar hoop, the fixing screw rod is welded to a steel structure component, the steel bar hoop is wound around the outer wall of the steel structure component, the welding sleeves at two ends of the steel bar hoop can freely move back and forth, and the joint of the welding sleeves and the fixing screw is reinforced by the fixing screws. When the reinforcement device of the stiff cylinder and shear wall composite structure formwork is used, the welding sleeves are welded to the two ends of the steel bar hoop, the fixing screw rod is fixed on the steel structure component in a penetrated welding manner, a formwork reinforcement system is mounted, then the steel bar hoop is mounted, the fixing screw rod penetrates through the welding sleeves, and is reinforced by using the fixing screws, so that the shortcoming of incapability ofreinforcing irregular stiff core cylinder in the conventional construction method is overcome and the fixing screw rod can be reused. The reinforcement device of the stiff cylinder and shear wall composite structure formwork has the characteristics of good reinforcement effect, low cost, excellent economic benefits and convenient operation, and can be widely used in various stiff structural engineering.