The invention discloses an assembling device for a power battery module. The assembling device includes a combined frame, a supporting frame, fixed foot plates and a butt joint clamping block; the supporting frame is fixedly mounted on the inner side of the combined frame, two sets of connecting supports are fixedly mounted on the outer surface of the upper end of the combined frame, and the fixedfoot plates are fixedly mounted on the outer surfaces of the upper ends of the connecting supports; and hydraulic rods are fixedly mounted in the middles of the inner sides of the fixed foot plates,fixed side rods are fixedly mounted on positions, close to two sides of the hydraulic rods, at the upper ends of the fixed foot plates, the outer surfaces of the bottoms of the fixed side rods are fixedly sleeved with fixed clamping sleeves, and the fixed side rods are fixedly connected with the fixed foot plates through the fixed clamping sleeves. The assembling device for the power battery module is provided with a movable adjusting structure, so that the application range of the assembling device is widened, and the assembling device is suitable for battery modules of different types; and meanwhile, the assembling device is provided with an auxiliary fixing structure, so that inclination of the battery modules in an assembling process is avoided, and the stability of the battery modulesis improved.