A method of determining the number of Acknowledgment/Non-Acknowledgment, ACK/NACK, feedback bits, wherein when carriers with different Time Division Duplex, TDD, uplink/downlink configurations are aggregated for a User Equipment, UE, or when aggregated carriers comprise at least one Frequency Division Duplex, FDD, carrier and at least one TDD carrier and the TDD carrier acts as Primary Component Carrier, PCC, and if the UE feeds back ACK/NACK over a Physical Uplink Shared Channel, PUSCH, with a corresponding Physical Downlink Control Channel, PDCCH, the PDCCH including a Downlink Assignment Index, DAI, field, the method comprising: judging whether there is a first category of carrier among carriers aggregated for a UE, wherein the first category of carrier refers to a carrier with a reference TDD uplink/downlink configuration being a first category of TDD uplink/downlink configuration and the first category of TDD uplink/downlink configuration refers to a TDD uplink/downlink configuration indicating a set of indexes, associated with an uplink sub-frame, in which the number of elements is larger than 4; or the first category of carrier refers to a carrier on which the number of downlink sub-frames for which ACK/NACK needs to be fed back among a set of downlink sub-frames is larger than 4, wherein the set of downlink sub-frames is determined according to a set of indexes, associated with an uplink sub-frame, indicated by a reference TDD uplink/downlink configuration of the carrier; wherein the reference TDD uplink/downlink configuration refers to a TDD uplink/downlink configuration for determining a relationship between a downlink sub-frame on the carrier and an uplink sub-frame in which ACK/NACK feedback information of the downlink sub-frame is transmitted; if there is the first category of carrier, then determining by a first category of scheme the number of downlink sub-frames, on each carrier c aggregated for the UE, for which ACK/NACK needs to be fed back in the current uplink sub-frame; if there is no first category of carrier, then obtaining W DAI UL, and M c of each carrier c aggregated for the UE, and determining the number B c DL of downlink sub-frames, on each carrier c aggregated for the UE, for which ACK/NACK needs to be fed back in the current uplink sub-frame, to be B c DL = min W DAI UL M c; and determining the number of ACK/NACK feedback bits to be fed back in the current uplink sub-frame according to the number of downlink sub-frames on each carrier c for which ACK/NACK needs to be fed back in the current uplink sub-frame; wherein W DAI UL represents a value indicated in the DAI field in the PDCCH; M c represents the number of downlink sub-frames, for which ACK/NACK needs to be fed back, among the set of downlink sub-frames on the carrier c determined by the set of indexes, associated with the current uplink sub-frame, indicated by the reference TDD uplink/downlink configuration of the carrier c. judging whether there is a first category of carrier among carriers aggregated for a UE, wherein the first category of carrier refers to a carrier with a reference TDD uplink/downlink configuration being a first category of TDD uplink/downlink configuration and the first category of TDD uplink/downlink configuration refers to a TDD uplink/downlink configuration indicating a set of indexes, associated with an uplink sub-frame, in which the number of elements is larger than 4; or the first category of carrier refers to a carrier on which the number of downlink sub-frames for which ACK/NACK needs to be fed back among a set of downlink sub-frames is larger than 4, wherein the set of downlink sub-frames is determined according to a set of indexes, associated with an uplink sub-frame, indicated by a reference TDD uplink/downlink configuration of the carrier; wherein the reference TDD uplink/downlink configuration refers to a TDD uplink/downlink configuration for determining a relationship between a downlink sub-frame on the carrier and an uplink sub-frame in which ACK/NACK feedback information of the downlink sub-frame is transmitted; if there is the first category of carrier, then determining by a first category of scheme the number of downlink sub-frames, on each carrier c aggregated for the UE, for which ACK/NACK needs to be fed back in the current uplink sub-frame; if there is no first category of carrier, then obtaining W DAI UL, and M c of each carrier c aggregated for the UE, and determining the number B c DL of downlink sub-frames, on each carrier c aggregated for the UE, for which ACK/NACK needs to be fed back in the current uplink sub-frame, to be B c DL = min W DAI UL M c; and determining the number of ACK/NACK feedback bits to be fed back in the current uplink sub-frame according to the number of downlink sub-frames on each carrier c for which ACK/NACK needs to be fed back in the current uplink sub-frame; wherein W DAI UL represents a value indicated in the DAI field in the PDCCH; M c represents the number of downlink sub-frames, for which ACK/NACK needs to be fed back, among the set of downlink sub-frames on the carrier c determined by the set of indexes, associated with the current uplink sub-frame, indicated by the reference TDD uplink/downlink configuration of the carrier c.