A loop circuit based automatic time synchronization method of a watch. The method comprises: step 1, adjusting a hand to a pre-set position; step 2, acquiring a current time; and step 3, sending the current time to the watch, and adjusting the hand to the current accurate time. Step 1 comprises the following steps: the watch comprises a surface, and the surface is provided with an opening; a flexible restorable conductor is provided at a position, directly facing the opening of the surface, of a machine core of the watch; the length of the conductor extending out of the opening is greater than the height of any hand to the surface; the conductor is in an open circuit, and when starting an automatic synchronization program of the watch, when the hand contacts the conductor, the open circuit is closed; when the processor detects that the open circuit is closed, the processor controls a drive motor of the hand contacting the conductor to drive the hand to rotate by a rotation threshold and stop at the pre-set position.