The present invention provides a battery module assembly comprising: two or more battery modules comprising two or more plate-shaped battery cells stacked vertically so that electrode leads are aligned in one direction, and provided with terminal portions for connecting to the outside; a base plate comprising module housing portions, on the upper surface of which the battery modules are loaded so that electrode terminals are aligned in one direction, and provided on the outer peripheral surface thereof with side walls curved upward; an upper cover plate comprising side walls curved downward on two sides of the electrode terminals on the battery modules, and defining the upper surface of the module assembly by being fixed on top of the base plate; a plate-shaped assembly cover, loaded on top of the upper surface of the battery modules and combined with the battery modules by coupling, for fixing a cable; and an electrically insulated module cover installed on top of the electrode leads on the battery cells and fixedly coupled to the base plate and the assembly cover.