A method for implementing time synchronization in an Optical Transport Network, OTN, the method comprises: generating, by a first time synchronization device of a master device, a time synchronization message, writing into the time synchronization message a first timestamp T1 at which the time synchronization message is generated, and adding to a correction domain of the time synchronization message a complement of local counting time t1 at which the time synchronization message exits from the first time synchronization device; receiving, by a first service transport device of the master device, the time synchronization message from the first time synchronization device, adding to the correction domain of the time synchronization message, local counting time t2 at which the time synchronization message exits from the first service transport device, and sending the time synchronization message to a slave device; receiving, by the master device, a delay request message which has been subjected to a third correction and includes a third timestamp T3; sending, by the first service transport device, local counting time t3 at which the delay request message is received as well as the delay request message to the first time synchronization device; and determining, by the first time synchronization device, local counting time t4 at which the delay request message is received, adding a difference value between t4 and t3 to the correction domain of the delay request message, generating the delay response message, adding to the delay response message the fourth timestamp T4 at which the delay response message is generated and the correction domain of the delay request message, and sending the delay response message to the slave device through the first service transport device. generating, by a first time synchronization device of a master device, a time synchronization message, writing into the time synchronization message a first timestamp T1 at which the time synchronization message is generated, and adding to a correction domain of the time synchronization message a complement of local counting time t1 at which the time synchronization message exits from the first time synchronization device; receiving, by a first service transport device of the master device, the time synchronization message from the first time synchronization device, adding to the correction domain of the time synchronization message, local counting time t2 at which the time synchronization message exits from the first service transport device, and sending the time synchronization message to a slave device; receiving, by the master device, a delay request message which has been subjected to a third correction and includes a third timestamp T3; sending, by the first service transport device, local counting time t3 at which the delay request message is received as well as the delay request message to the first time synchronization device; and determining, by the first time synchronization device, local counting time t4 at which the delay request message is received, adding a difference value between t4 and t3 to the correction domain of the delay request message, generating the delay response message, adding to the delay response message the fourth timestamp T4 at which the delay response message is generated and the correction domain of the delay request message, and sending the delay response message to the slave device through the first service transport device.