The invention discloses a multipurpose combined backpack. The multipurpose combined backpack comprises a hard back pad, a backpack body which is detachably arranged on the hard back pad and straps, wherein a plurality of clamping holes are formed in the hard back pad; the backpack body and the straps are detachably arranged on the hard back pad through a plurality of buckles which are connected with the backpack body and the straps and matched with the clamping holes; a cross beam is arranged in the middle of the buckles; the buckles are connected with the backpack body or the straps through connection slings which are connected with the cross beam; and the buckles are capable of longitudinally penetrating through the clamping holes and can be transversely clamped at one sides of the clamping holes. The backpack body, the straps, a back base plate, a waist bag and a bottom support plate are detachably arranged on the hard back pad; and meanwhile, the backpack body is formed by upper and lower body parts which are detachably connected; therefore, the bags and accessories can be increased or decreased according to individual demand, the free combination according to individual demand can be realized, and one backpack is capable of satisfying different demands of backpack capacity and accessory combination.