Disclosed are a time synchronization method and system. The method comprises: an NE1 and the upstream nodes of the NE1 are classified into the first level, and the downstream nodes of the NE1 are classified into the second level, where the first level priority of the first level is higher than the second level priority of the second level; an NE3 connected to the NE1 through a PTP synchronization link in the downstream node receives a first device priority of the NE1 and the first level priority from the NE1; and after the NE3 receives the second device priority of an NE2 and the second level priority sent by the NE2 in the downstream nodes which is connected to the NE1 through the 1PPS+TOD synchronization link, determines that a clock parameter of the NE1 is optimal, and synchronizes the local clock to the NE1.