Embodiments of this application provide a time synchronization method and a device. The method includes: generating, by a first device, a first time synchronization frame according to a first coding scheme, where the first time synchronization frame includes a first frame header and a first time of day TOD, the first frame header carries an identifier of the first coding scheme, and the first coding scheme defines a boundary of the first time synchronization frame and a location of the first TOD in the first time synchronization frame; and sending, by the first device, the first time synchronization frame to a second device by using a first single line, so as to trigger the second device to identify the first time synchronization frame according to the identifier of the first coding scheme, obtain the first TOD from the first time synchronization frame, and trace a time of the first device according to the first TOD. With the time synchronization method and the device in the embodiments of this application, line resources can be saved.