A battery module assembly includes a front frame and a rear frame installed on the front and rear surfaces of the cell assembly and configured to mold a bus bar for electrically connecting battery cells included in the cell assembly, a left end plate and a right end plate respectively covering both side surfaces of the cell assembly, an upper clamp and a lower clamp disposed over an upper portion and a lower portion of the cell assembly, respectively clamping an upper portion and a lower portion of each of the left end plate and the right end plate, and pressing both side surfaces of the cell assembly disposed between the left end plate and the right end plate, and a front cover and a rear cover covering the front frame and the rear frame. A long hole formed in an upper portion and a lower portion of the front cover and the rear cover, and a pipe disposed on an inner perimeter surface of the long hole.