A weight lifting system includes a handle unit having a handle bar, two head units attached to two end sections of the handle bar in a manner that allows the two head units to rotate about a longitudinal axis of the handle bar, two screw rods disposed through holes in the two head units into hollow sections in the handle bar, wherein the two screw rods have threads of opposite directions, two thread-engaging mechanisms fixedly disposed at the two end sections of the handle bar to fit snugly on the threads of the two screw rods, and a lock mechanism disposed in a head unit for controlling rotation of the handle bar; and a plurality pairs of weight discs, wherein each of the weight discs has a center hole configured to accommodate one of the two screw rods.