An uplink synchronization method in a multi-carrier system, the method comprising: selecting, by an eNodeB, one or more first component carriers which have not acquired uplink synchronization with the eNodeB from a plurality of component carriers supported by a user equipment; acquiring, by the eNodeB, a Timing Advance, TA, of the first component carrier; and transmitting, by the eNodeB, the TA of the first component carrier to the user equipment to instruct the user equipment to perform uplink transmission over the first component carrier according to the TA, wherein acquiring by the eNodeB the TA of the first component carrier is performed according to one of the following first or second approach: in the first approach, the eNodeB transmits random access related instruction signaling which includes an identifier of the first component carrier to the user equipment, and the eNodeB calculates the TA for the user equipment to perform uplink transmission over the first component carrier upon reception of a random access preamble transmitted from the user equipment to the eNodeB over the first component carrier; and in the second approach, the eNodeB determines a second component carrier among the plurality of component carriers which has acquired uplink synchronization with the eNodeB and determines a TA used to perform uplink transmission over the second component carrier as the TA used to perform uplink transmission over the first component carrier; wherein after the user equipment performs uplink transmission over the first component carrier according to the TA and classifies the respective first component carriers into groups such that TA differences of the first component carriers in one group do not exceed a preset threshold, the method further comprises: transmitting, by the eNodeB, a TA command to the user equipment and starting a TAT, maintained by the eNodeB, corresponding to the group at a preset interval of time which is shorter than a length of timing of the TAT; retransmitting, by the eNodeB, a TA command to the user equipment and restarting the TAT, maintained by the eNodeB, corresponding to the group, when the eNodeB receives a NACK message transmitted from the user equipment due to incorrect reception of the TA command; restarting the TAT, maintained by the eNodeB, corresponding to the group, when the eNodeB receives an ACK message from the user equipmer due to correct reception of the TA command; and determining by the eNodeB that the respective first component carriers in the group are out of synchronization when the TAT maintained by the eNodeB corresponding to the group is time out. selecting, by an eNodeB, one or more first component carriers which have not acquired uplink synchronization with the eNodeB from a plurality of component carriers supported by a user equipment; acquiring, by the eNodeB, a Timing Advance, TA, of the first component carrier; and transmitting, by the eNodeB, the TA of the first component carrier to the user equipment to instruct the user equipment to perform uplink transmission over the first component carrier according to the TA, in the first approach, the eNodeB transmits random access related instruction signaling which includes an identifier of the first component carrier to the user equipment, and the eNodeB calculates the TA for the user equipment to perform uplink transmission over the first component carrier upon reception of a random access preamble transmitted from the user equipment to the eNodeB over the first component carrier; and in the second approach, the eNodeB determines a second component carrier among the plurality of component carriers which has acquired uplink synchronization with the eNodeB and determines a TA used to perform uplink transmission over the second component carrier as the TA used to perform uplink transmission over the first component carrier; transmitting, by the eNodeB, a TA command to the user equipment and starting a TAT, maintained by the eNodeB, corresponding to the group at a preset interval of time which is shorter than a length of timing of the TAT; retransmitting, by the eNodeB, a TA command to the user equipment and restarting the TAT, maintained by the eNodeB, corresponding to the group, when the eNodeB receives a NACK message transmitted from the user equipment due to incorrect reception of the TA command; restarting the TAT, maintained by the eNodeB, corresponding to the group, when the eNodeB receives an ACK message from the user equipmer due to correct reception of the TA command; and determining by the eNodeB that the respective first component carriers in the group are out of synchronization when the TAT maintained by the eNodeB corresponding to the group is time out.