A method for assigning ACK channels to a user, which is used to feed back ACKs of N downlink sub-frames in one uplink sub-frame in a time division duplex, TDD, system, the method comprising: dividing reserved ACK channels into N blocks, each downlink sub-frame of the N downlink sub-frames corresponds to one block in a preset sequence, wherein the preset sequence is a sequence that a special sub-frame is placed at a last position, or the preset sequence is a sequence that the sub-frame with the maximum actual value of n is placed at a foremost position; dividing each block into max{ Mi} or Mi sub-blocks, the sub-blocks belonging to different blocks being interleaved and sub-blocks which are from the different blocks and mapped to a same control channel element, CCE, set of different sub-frames are arranged sequentially according to the preset sequence; and assigning the ACK channels to the downlink sub-frames by mapping CCE sets with labels of {0, 1,..., N CCE, 1 -1-△1}, { N CCE, 1 -△1, N CCE, 1 -△1+1,..., N CCE, 2 -1-△2},..., { N CCE,max{ Mi}-1 -△max{Mi}-1, N CCE,max{ Mi}-1 -△max{Mi}-1+1,..., N CCE, max{ Mi} -1} within each downlink sub-frame to the max{ Mi} sub-blocks of the block associated with downlink sub-frame of label i; or assigning (b) the ACK channels to the downlink sub-frames by mapping CCE sets with labels of {0, 1,..., N CCE, 1 -1-△1}, { N CCE, 1 -△1, N CCE, 1 -△1+1,..., N CCE,2 -1-△2},..., { N CCE,Mi -1 -△Mi-1, N CCE,Mi -1 -△Mi-1+1,..., N CCE,Mi -1} within each downlink sub-frame to the Mi sub-blocks of the block associated with downlink sub-frame of label i; wherein △1, △2,..., △max{Mi}-1 are adjustment factors, the N being a positive integer, the Mi represents a maximum possible value of n for a downlink sub-frame with a label of i among N downlink sub-frames, the i=0, 1,..., N-1, the max{ Mi} represents a maximum value of Mi, the N CCE,max{ Mi} represents the number of CCEs in the downlink sub-frame when n is equal to max{ Mi}, the N CCE, Mi represents the number of CCEs in the downlink sub-frame when n is equal to Mi, the n is the number of symbols occupied by a physical downlink control channel, PDCCH. dividing reserved ACK channels into N blocks, each downlink sub-frame of the N downlink sub-frames corresponds to one block in a preset sequence, wherein the preset sequence is a sequence that a special sub-frame is placed at a last position, or the preset sequence is a sequence that the sub-frame with the maximum actual value of n is placed at a foremost position; dividing each block into max{ Mi} or Mi sub-blocks, the sub-blocks belonging to different blocks being interleaved and sub-blocks which are from the different blocks and mapped to a same control channel element, CCE, set of different sub-frames are arranged sequentially according to the preset sequence; and assigning the ACK channels to the downlink sub-frames by mapping CCE sets with labels of {0, 1,..., N CCE, 1 -1-△1}, { N CCE, 1 -△1, N CCE, 1 -△1+1,..., N CCE, 2 -1-△2},..., { N CCE,max{ Mi}-1 -△max{Mi}-1, N CCE,max{ Mi}-1 -△max{Mi}-1+1,..., N CCE, max{ Mi} -1} within each downlink sub-frame to the max{ Mi} sub-blocks of the block associated with downlink sub-frame of label i; or assigning (b) the ACK channels to the downlink sub-frames by mapping CCE sets with labels of {0, 1,..., N CCE, 1 -1-△1}, { N CCE, 1 -△1, N CCE, 1 -△1+1,..., N CCE,2 -1-△2},..., { N CCE,Mi -1 -△Mi-1, N CCE,Mi -1 -△Mi-1+1,..., N CCE,Mi -1} within each downlink sub-frame to the Mi sub-blocks of the block associated with downlink sub-frame of label i; wherein △1, △2,..., △max{Mi}-1 are adjustment factors, the N being a positive integer, the Mi represents a maximum possible value of n for a downlink sub-frame with a label of i among N downlink sub-frames, the i=0, 1,..., N-1, the max{ Mi} represents a maximum value of Mi, the N CCE,max{ Mi} represents the number of CCEs in the downlink sub-frame when n is equal to max{ Mi}, the N CCE, Mi represents the number of CCEs in the downlink sub-frame when n is equal to Mi, the n is the number of symbols occupied by a physical downlink control channel, PDCCH.