A method of clock transmission between networks and an apparatus of clock transmission are disclosed, in which a second group of information corresponding to a clock transferred by a first network equipment based on a first protocol, and the second group of information corresponding to a clock transferred by a second network equipment based on a second protocol are acquired, and a source selection is performed in a united way by adopting a source selection manner based on the second protocol according to the second group of information. Therefore, the equipment in different types of networks can conveniently select a clock with a higher class from clocks transferred based on different protocols, so as to realize a normalization management on the clocks transferred based on different protocols.