The invention discloses a nested disc cam focusing mechanism, belonging to the field of cam focusing. The nested disc cam focusing mechanism provided by the invention solves the problems that a focusing mechanism of a nested optical system is complicated, the focusing precision is low and the like. The mechanism mainly comprises a first microscope base, a second microscope base, a third microscope base, a fourth microscope base, a fifth microscope base, a sixth microscope base, a slider, a guide rail, disc cams, a driven member, a spring and the like, wherein the first microscope base and the sixth microscope base form a first microscope base group; the second microscope base and the fifth microscope base form a second microscope base group; the third microscope base and the fourth microscope base form a third microscope base group; the microscope base groups move relatively along the direction of an optical axis to form a nested structure; three disc cams control the moving rules of the three groups of nested microscope bases through the driven member respectively and change the positions of the three groups of nested microscope bases so as to realize focusing of the whole system; and moreover, due to the independent microscope base and disc cam structure, compared with a cylindrical cam, the structure is simple, the processing cost is low, and the focusing precision is high.