Embodiments of this application provide a method, apparatus, and system for determining a synchronization cycle, and relate to the communications field, to determine a proper synchronizing cycle, so that air interface bandwidth resources are saved during clock synchronization in an industrial factory, energy consumption of UE is reduced, and battery power is saved. The method includes: A network device obtains a crystal oscillator frequency offset f1 of UE; the network device obtains a crystal oscillator frequency offset f2 of an AN; the network device obtains a service synchronization precision requirement t of the UE; and the network device calculates a synchronization cycle of clock synchronization between the UE and the AN based on the obtained f1, f2, and t.