Weight adjustable dumbbell and using method thereof

A weight adjustable dumbbell, comprising a connecting bar and a supporting base, wherein two sides of a top surface of the supporting base are defined with a receiving groove, respectively, a plurality of dumbbell plates opposite to each other are provided in the receiving grooves along an axial direction, a notch is defined on each of the dumbbell plates capable to inserting the connecting bar, a slot opposite to the connecting bar is defined on an inner wall of the notch, a plurality of fasteners opposite to the dumbbell plates are provided on the connecting bar along the axial direction, the fasteners at an end of the connecting bar are arranged spirally along the axial direction, and are arranged at equal angles about the axis of the connecting bar, the plurality of fasteners are capable of connecting to the slot of the dumbbell plates sequentially via rotating the connecting bar, and the dumbbell plates are detachably connected to limiting parts capable of limiting the rotation of the connecting bar.