The invention discloses a space-adjustable assembly cabinet for kitchens and baths. The cabinet comprises a cabinet body, a partition plate and limiting sliding grooves, the partition plate is vertically arranged at the inner side of the cabinet body, the limiting sliding grooves are connected to the positions, corresponding to the inner side of the cabinet body, of the upper end and the lower endof one side of the partition plate through screws, and sliding bases are arranged at the positions, close to the limiting sliding grooves, of the upper end and the lower end of the partition plate. The partition plate, the sliding bases, locking screws, the limiting sliding grooves, fixing strips, an inclined inserting groove, a supporting plate base and a supporting plate block are arranged, therefore, when the assembly cabinet is used, the space at the inner side of the cabinet can be adjusted according to actual use requirements, the space at the inner side of the cabinet can be effectively used, the actual use needs are met, through the arrangement of a damp-proof box and a ventilation net, when the cabinet is used, damp-proof treatment is conducted on the inner side of the cabinet through damp-proof agents stored on the inner sides of the damp-proof box and the ventilation net, articles stored on the inner side of the cabinet are not prone to being affected with damp, and the storage quality of the articles is guaranteed.