The embodiment of the invention discloses a 3D printing auxiliary method and device. The method comprises the steps that supporting liquid is provided, and the supporting liquid is used for providing buoyancy support for a printed object which is immersed into the supporting liquid at least in part in the printing process and keeping the printed object in the floating or suspending state in the supporting liquid. According to the technical scheme, printing of a supporting structure can be omitted at least in part, and printing materials and printing time are saved; the printed object is evenly and softly supported through the supporting liquid, the printed object is comprehensively supported, meanwhile, the shape of the printed object which is not completely cured is not prone to be damaged, and the printing finished product quality is improved. On the premise that liquid supporting exists, the printing face is changed, and a high-quality finished product is more easily obtained, operation like rotation can be conveniently performed on the printed object, and the shape of the printed object which is not completely cured is not prone to be damaged.