The invention discloses a planetary gear train of a double-tourbillion mechanical watch; wherein, a planetary gear gasket is fixed with a planetary gear shaft by a planetary screw; the matching screwing direction of an internal thread of the planetary gear shaft and an external thread of the planetary screw is identical with the direction of the torque of the planetary gear; planetary gear sets are arranged on a second central gear gasket; a first central gear gasket is meshed with the planetary gear gasket; a third central gear shaft and a third central gear gasket are coaxially arranged on a second central gear shaft; the third central gear shaft is meshed with the planetary gear shaft. The planetary gear train has the benefits that as four planetary gears are arranged, the moment which is oscillated by a planetary carrier and generated by meshing of the planetary gear and an input shaft can be counteracted in four directions; the structure all adopts external gearing and is convenient in processing, in particular, the planetary carrier is used as one of the input gears, thereby reducing the overall axial dimension of the planet structure and the thickness of a clock mechanism; in addition, the screw is used for fixing the planetary gear gasket and the planetary gear shaft so that the planetary gear gasket and the planetary gear shaft can be correctly assembled and reliably meshed when the planetary mechanism is assembled, thereby ensuring that the relative positions of the arranged gear teeth are not changed.