The present invention discloses a method and Ethernet device for clock synchronization, a method for clock synchronization in an entire Ethernet, and the relevant Ethernet. The method for clock synchronization in an Ethernet device includes: the PHY layer unit of the Ethernet device extracts a clock from the data sent by the receive unit; the MAC layer unit makes adjustments to the extracted clock according to the local clock and takes the adjusted clock as the transmit clock of the Ethernet device. The method for clock synchronization in an entire Ethernet includes: clocks of all Ethernet devices are synchronized to the clock generated by the Ethernet device at the highest level. The invention provides a method for clock synchronization so that sending and receiving of clocks in Ethernet devices can be synchronized and clock synchronization can be realized in the entire Ethernet.