Provided is a sectional-type secondary mirror high-stability support structure, which comprises a first front lens cone (1), a second front lens cone (2) and a secondary mirror support assembly (3). The secondary mirror support assembly (3) comprises spoke plate assemblies (4) and a secondary mirror frame (5). Each spoke plate assembly (4) comprises a spoke plate (10) and a spoke plate base. One end of the spoke plate (10) is connected with the spoke plate base, and the other end thereof is connected with the secondary mirror frame (5) and is tangent to the circular secondary mirror frame (5); each spoke plate base is fixedly arranged at one end of the second front lens cone (2); and the other end of the second front lens cone (2) is connected with the first front lens cone (1). The support structure realizes high-stability secondary mirror support through the composite-material lens cones and a flexible spoke plate structure; and the support structure also adopts the spoke plate structure in a three-layer sandwich structure, so that weight is reduced, structure rigidity is improved, and thermal stress is unloaded to some extent.