An improved counterweight module of a weight trainer having two vertical guide rods as well as top, bottom and intermediate counterweight blocks superimposed along the vertical guide rods. It is mainly characterized in that a liner ring assembly is only assembled onto the bottom and top counterweight blocks. The liner ring assembly has upper liner rings set into the top counterweight block and lower liner rings set into the bottom counterweight block. The annular rings of the upper and lower liner ring are mated slidably with two vertical guide rods. Moreover, a guide rod pulling portion is set onto every intermediate counterweight block for penetration of the vertical guide rod. There is a spacing between the guide rod pulling portion and vertical guide rods. The superimposition surface of the counterweight block is provided with a mating portion to enable limitation of every intermediate counterweight block.