The present invention provides a method for reconfiguring an aggregated cell, which includes that: a network side device judges whether the aggregated cell of a user equipment (UE) needs to be changed in the cell set in which the carriers can be aggregated; when the judgment result is that the change is needed, the network side device transmits a radio resource control (RRC) connection reconfiguration message to the UE, and the RRC connection reconfiguration message carries the change information of the aggregated cell of the UE; the UE receives the RRC connection reconfiguration message, and reconfigures the aggregated cell according to the RRC connection reconfiguration message. In the present invention, for the LTE-A system, when the aggregated cell of UE which supports the carrier aggregation changes within the same cell set in which the carriers can be aggregated, the aggregated cell of the UE can be reconfigured; and the same access stratum (AS) key is used to perform the security processing procedure for the data, which enables the uninterrupted transmission for the data.