Methods, systems, and apparatus for clock synchronization are provided. In one aspect, a clock synchronization method includes: receiving, by a terminal and from an access network device, information about N clock domains, determining, by the terminal, M clock domains that are associated with the terminal and that are in the N clock domains, and separately performing, by the terminal, clock synchronization with clock sources of the M clock domains based on information about the M clock domains. Information about a clock domain includes first time information and a clock domain number of the clock domain. The first time information includes a time of a clock source of the clock domain when the access network device sends the information about the clock domain. The clock domain number identifies the clock domain. N is an integer greater than 1, and M is an integer greater than 1.