The invention discloses a device for assembling a cabinet machine air conditioner shell. The device comprises a base, a push-pull mechanism, an overturning mechanism and a clamping mechanism; an overturning shaft is arranged on the inner side of the upper portion of the base; the push-pull mechanism comprises a first cylinder which is connected with a first push-pull sliding block; the first push-pull sliding block is provided with a first guiding rod and a push-pull lower rotating shaft; the overturning mechanism comprises a rotary bracket; a conveying belt is arranged on the short edge part of the rotary bracket; a push-pull upper rotating shaft is arranged at the bottom of the long edge part of the rotary bracket; a push-pull rod is arranged below the rotary bracket; the clamping mechanism comprises a second cylinder which is connected with a second push-pull sliding block; a second guiding rod is arranged on the second push-pull sliding block in a penetrating manner; the second push-pull sliding block is further connected with a synchronous belt with the two ends provided with synchronous wheels; the synchronous wheel on one side is fixedly connected with a first clamping frame; and the synchronous wheel on the other side is fixedly connected with a driving gear engaged with a driven gear. The invention further provides an assembling method using the device. The device for assembling the cabinet machine air conditioner shell is stable in action and reliable in work, the manual labor intensity is further reduced, and the production efficiency is improved.