The present invention relates to a structure of a screw-free adaptation rack, which includes a main casing including a carrying section to define an upper portion of the main casing as a primary accommodation space and a lower portion as a secondary accommodation space. A partition plate is arranged in the primary accommodation space for division into a first receiving space and a second receiving space. A retention mechanism retains at least one 2.5-inch hard drive in the primary accommodation space. The secondary accommodation space has two sidewalls with a pair of bumps and a pair of through apertures formed therein so that with position adjustment of a retained object, the bumps are fit into and thus retain the retained object, allowing the present invention to readily receive and retain a hard drive and a 3.5-inch floppy disk drive in a screw-free manner for extensive applications to various specifications.