The present invention provides a method, an apparatus, and a system for time synchronization of an xDigital Subscriber Line (xDSL). The method includes: transmitting, by a customer premises equipment (CPE), a first symbol to a central office (CO) equipment, and obtaining time Ts2 indicating the moment that the first symbol is transmitted; receiving, by the CPE, a second symbol transmitted by the CO, and obtaining time Ts1 indicating the moment that the second symbol is received; obtaining, by the CPE obtains time Tm2 indicating the moment that the first symbol is received by the CO and time Tm1 indicating the moment that the second symbol is transmitted by the CO; the CPE calculates an offset between a clock of the CPE and a clock of the CO according to Ts1, Ts2, Tm1, Tm2 and a delay of the CPE; and the CPE adjusts the clock of the CPE according to the offset to achieve synchronization. According to the present invention, by adjusting the time of the clock of the CPE and the time of the clock of the CO, the offset between the clock of the CPE and the clock of the CO can be obtained accurately to effectively achieve time synchronization between the CPE and the CO.