Disclosed are a method for determining a hybrid automatic repeat request (HARQ) process number (HPN) allocated to downlink link (DL) data, a method for notifying a HPN allocated to the DL data, a method for allocating a HPN to DL data, a base station, and a user equipment. The method for determining a HPN allocated to DL data includes: receiving DL control information (DCI) associated with DL data; determining, according to the DCI, whether the DL data satisfies a predetermined condition; and when the DL data satisfies the predetermined condition, determining the HPN allocated to the DL data based on a HPN field and an additional field in the DCI. Alternatively, the method for determining a HPN allocated to DL data includes: receiving DCI related to current DL data; determining whether HPN fields in the DC are predetermined values indicating at least a first HPN and a second HPN; and when it is determined that the HPN fields are predetermined values, determining a HPN allocated to the current DL data, according to a reception state of DL data sent before the current DL data. Accordingly, overheads and power consumption are not increased while more than 8 HARQ processes are supported.