A method for synchronizing a network device includes: receiving, by the network device, a first SSM and a second SSM, where the first SSM carries a first SSM code for indicating a quality level of a first clock source and a first eSSM code for indicating the quality level of the first clock source, and the second SSM carries a second SSM code for indicating a quality level of a second clock source and a second eSSM code for indicating the quality level of the second clock source. When a value of the first SSM code is less than a value of the second SSM code, the network device calibrates a frequency of the network device based on a timing signal of the first clock source.