A method for uplink synchronization in a multi-carrier system includes the following steps: a base station selects one or more first component carriers, which do not establish the uplink synchronization with the base station, from multiple component carriers supported by a terminal; then the base station obtains Timing Advance (TA) needed by the terminal to perform the uplink transmission on the first component carriers, and sends the TA information to the terminal; the terminal performs the uplink transmission on said first component carriers according to said TA. The application of the present invention enables the establishment of uplink synchronization between the base station and the user equipment in multi-carrier system.