A data transmission apparatus, comprising: a receiving module, configured to receive a downlink data packet sent by a core network device; a sending module, configured to send a first downlink data packet in the downlink data packet to user equipment UE, and send a second downlink data packet in the downlink data packet to a Wireless Fidelity access point wifi AP through an Xw interface, so that the wifi AP is enabled to send the second downlink data packet to the UE, wherein a base station is enabled to manage a wifi radio resource by using the Xw interface; and a communication adaptation layer establishment module, configured to establish a communication adaptation layer between the base station and the wifi AP, wherein the communication adaptation layer is used to establish a mapping relationship from a radio bearer RB of a cellular network to a wifi access category AC of a wireless local area network, wherein the sending module is further configured to: send, to the wifi AP, a request message for adding a wifi secondary cell wifiSCell, and send, to the user equipment UE, a configuration message for adding a wifi secondary cell wifiSCell, wherein the request message for adding a wifiscell or the configuration message for adding a wifiSCell comprises information about the communication adaptation layer and at least one of the following: a quantity of required channels, a channel number, a channel frequency, and a channel bandwidth. a receiving module, configured to receive a downlink data packet sent by a core network device; a sending module, configured to send a first downlink data packet in the downlink data packet to user equipment UE, and send a second downlink data packet in the downlink data packet to a Wireless Fidelity access point wifi AP through an Xw interface, so that the wifi AP is enabled to send the second downlink data packet to the UE, wherein a base station is enabled to manage a wifi radio resource by using the Xw interface; and a communication adaptation layer establishment module, configured to establish a communication adaptation layer between the base station and the wifi AP, wherein the communication adaptation layer is used to establish a mapping relationship from a radio bearer RB of a cellular network to a wifi access category AC of a wireless local area network, wherein the sending module is further configured to: send, to the wifi AP, a request message for adding a wifi secondary cell wifiSCell, and send, to the user equipment UE, a configuration message for adding a wifi secondary cell wifiSCell, wherein the request message for adding a wifiscell or the configuration message for adding a wifiSCell comprises information about the communication adaptation layer and at least one of the following: a quantity of required channels, a channel number, a channel frequency, and a channel bandwidth. send, to the wifi AP, a request message for adding a wifi secondary cell wifiSCell, and send, to the user equipment UE, a configuration message for adding a wifi secondary cell wifiSCell, wherein the request message for adding a wifiscell or the configuration message for adding a wifiSCell comprises information about the communication adaptation layer and at least one of the following: a quantity of required channels, a channel number, a channel frequency, and a channel bandwidth.