A method for sending an acknowledgement includes: sending first subframe ratio information and second subframe ratio information to a UE; reserving a first PHICH resource set in a first acknowledgement subframe set; reserving a second PHICH resource set in an acknowledgement subframe, in which the first PHICH resource set does not exist, of a second acknowledgement subframe set; receiving uplink data sent by the UE; determining an acknowledgement subframe for the uplink data; and sending an acknowledgement to the UE by using a PHICH resource in the first PHICH resource set if the first PHICH resource set exists in the acknowledgement subframe, or sending an acknowledgement to the UE by using a PHICH resource in the second PHICH resource set if the first PHICH resource set does not exist in the acknowledgement subframe. PHICH resource overhead of a system is lowered and data transmission for the user equipment is ensured.