A dual-shaft synchronous movement device and an assembling method thereof. The dual-shaft synchronous movement device includes a first shaft and a second shaft, which are assembled with each other and synchronously rotatable. The invention includes providing an assembling device and arranging on the assembling device a first rotor and a second rotor (or a third rotor and a fourth rotor) between which a drive section is wound; winding the drive section onto the first and second rotors (or the third and fourth rotors) in a tensioned state; and pushing the first and second rotors (or the third and fourth rotors) onto the first and second shafts. Through the first and second rotors (or the third and fourth rotors) and the drive section, when the first shaft is rotated, the second shaft is synchronously rotated.