The invention relates to an ultrasonic field assisted bulging device and method for a super-thin-wall complex curved surface microstructure. The bulging device comprises a base, a pressing plate connected with the base, a to-be-formed target arranged between the pressing plate and the base, and a forming mechanism making contact with the to-be-formed target to form the to-be-formed target. The forming mechanism is connected with an external driving mechanism. A groove for placing a soft mode medium is formed in the base. The upper surface of the soft mode medium is flush with the upper surfaceof the base. The groove for containing the soft mode medium is formed in the base, the soft mode medium is flush with the upper surface of the groove, and external force is exerted on the to-be-formed target and the soft mode medium as well after the to-be-formed target is placed between the base and the pressing plate, so the soft mode medium exert counter acting force on the to-be-formed target; and the soft mode medium is small in size change when bearing external force, and therefore the counter acting force exerted on the to-be-formed target is uniform, and the severe thinning or even breaking of the to-be-formed target caused by great local deformation can be avoided.