A method for sending an acknowledgement, comprising: sending, by a network-side device, first subframe ratio information and second subframe ratio information to a user equipment, wherein subframe ratios represented by the first subframe ratio information and the second subframe ratio information are different and wherein the subframe ratios represented by the first subframe ratio information and the second subframe ratio information are uplink and downlink subframe ratios; determining, by the network-side device, a first acknowledgement subframe set according to a first timing relation that is set for the first subframe ratio information, and reserving a first physical hybrid automatic repeat request indicator channel PHICH resource set in an acknowledgement subframe of the first acknowledgement subframe set; characterized by, determining, by the network-side device, a second acknowledgement subframe set according to a second timing relation that is set for the second subframe ratio information, and reserving a second PHICH resource set in an acknowledgement subframe, in which the first PHICH resource set does not exist, of the second acknowledgement subframe set, wherein the first PHICH resource set and the second PHICH resource set are reserved on the first service cell and the first service cell is the primary cell; receiving, by the network-side device, uplink data sent by the user equipment according to the second subframe ratio information; determining, by the network-side device, an acknowledgement subframe for the uplink data according to the second timing relation and a subframe for receiving the uplink data; and sending, by the network-side device by using a PHICH resource in the first PHICH resource set, an acknowledgement to the user equipment if the first PHICH resource set exists in the determined acknowledgement subframe for the uplink data, and sending, by the network-side device by using a PHICH resource in the second PHICH resource set, an acknowledgement to the user equipment if the first PHICH resource set does not exist in the acknowledgement subframe. sending, by a network-side device, first subframe ratio information and second subframe ratio information to a user equipment, wherein subframe ratios represented by the first subframe ratio information and the second subframe ratio information are different and wherein the subframe ratios represented by the first subframe ratio information and the second subframe ratio information are uplink and downlink subframe ratios; determining, by the network-side device, a first acknowledgement subframe set according to a first timing relation that is set for the first subframe ratio information, and reserving a first physical hybrid automatic repeat request indicator channel PHICH resource set in an acknowledgement subframe of the first acknowledgement subframe set; characterized by, determining, by the network-side device, a second acknowledgement subframe set according to a second timing relation that is set for the second subframe ratio information, and reserving a second PHICH resource set in an acknowledgement subframe, in which the first PHICH resource set does not exist, of the second acknowledgement subframe set, wherein the first PHICH resource set and the second PHICH resource set are reserved on the first service cell and the first service cell is the primary cell; receiving, by the network-side device, uplink data sent by the user equipment according to the second subframe ratio information; determining, by the network-side device, an acknowledgement subframe for the uplink data according to the second timing relation and a subframe for receiving the uplink data; and sending, by the network-side device by using a PHICH resource in the first PHICH resource set, an acknowledgement to the user equipment if the first PHICH resource set exists in the determined acknowledgement subframe for the uplink data, and sending, by the network-side device by using a PHICH resource in the second PHICH resource set, an acknowledgement to the user equipment if the first PHICH resource set does not exist in the acknowledgement subframe.