Data processing method, base station and ue

The present invention provides a data processing method, base station and UE. Said data processing method comprises: when a UE switches from source base station to target base station, said source base station sends data packets unacknowledged by said UE in downlink normal PDCP sequence number window and residual data packets in downlink extended PDCP sequence number window to target base station, said data packets in downlink normal PDCP sequence number window are excluded from said residual data packets in downlink extended PDCP sequence number window, wherein said downlink normal PDCP sequence number window is included in said downlink extended PDCP number sequence window, and said downlink extended PDCP sequence number window and said downlink normal PDCP sequence number window have the same starting position. Said data processing method avoids the problem of missing data packets when the UE switches from source base station using extended PDCP SN to target base station using normal PDCP SN.