The invention discloses a large-span cantilever type triaxial posture adjustment turntable for a spacecraft. The turntable comprises a supporting platform, an omnibearing travelling wheel system, a lifting system, an overturning system and a rotating mechanism, wherein the inner side of a C-type ring of an overturning rack is connected with the outer side of a rotating ring through a roller combination, the inner side of the C-type ring surrounds the outer side of the rotating ring, the rotating ring is adjusted to be in a proper assembling, testing or experimenting state, the spacecraft is locked dead by a locking device of the rotating ring, and then related working items of the spacecraft are carried out. According to the invention, opening assembly requirements of embedded products such as a high-thrust engine and the like as well as products such as narrow space pipes and the like of the spacecraft are met, reachability and convenience of operation are achieved, and the problem ofstructural deformation in the large-span and large-mass load cantilever state is solved.