The invention provides a support mechanism for a multi-side cylindrical achromatic prism and relates to a support mechanism belonging to the field of space imaging spectrum technologies. The invention aims at providing a support mechanism for a multi-side cylindrical achromatic prism and adopts the technical scheme that the support mechanism for the multi-side cylindrical achromatic prism comprises a gland, an outer drum, a gasket, a prism holder assembly and an achromatic prism assembly, wherein the prism holder assembly comprises an upper end surface, a jack screw hole, an end surface glue injecting hole, a vertical surface cavity wall pit, a big vertical surface, a small vertical surface, a lower end surface boss, a lower end surface and a pit washer; the achromatic prism assembly comprises a first prism, a prism spacer, a second prism, a lower clamp plate, a front clamp plate, a first composite washer and a second composite washer; the achromatic prism assembly is arranged in a cavity of the prism holder assembly, the prism holder assembly is arranged in the outer drum, the gland is inserted from the right end of the outer drum, and the bottom end of the gland is connected with the upper end surface in the prism holder assembly by a screw. The mechanism has the advantages of compact structure, wide temperature range and high surface precision and meets the development requirement of satellite borne spectrum imaging instruments.