A method for data transmission, comprising: updating, by an offload point device, when a first air interface is unavailable, connection context information corresponding to service(s) of a user equipment on the first air interface, wherein the user equipment is connected to a core network through a first access network via the first air interface, and the user equipment is further connected to the core network through a second access network via a second air interface; the method being characterized by further comprising sending, by the offload point device via the second air interface, a first message to the user equipment, wherein the first message carries updating information related to the updated connection context information, and the updating information is used by the user equipment to update connection context information currently corresponding to the service(s) on the first air interface; and performing, by the offload point device, data transmission with the user equipment according to the updated connection context information; wherein before the updating the connection context information corresponding to the service(s) of the user equipment on the first air interface, the method further comprises: receiving, by the offload point device, a second message via the second air interface that is generated and sent by the user equipment and used for indicating that the first air interface is unavailable, or receiving a second message that is generated and sent by an access device of the first air interface and used for indicating that the first air interface is unavailable; and determining, by the offload point device, that the first air interface is unavailable according to the second message; wherein the second message is application layer signaling encapsulated in a data packet, and a header of the data packet carries a predefined identity to indicate that the data packet carries application layer signaling. updating, by an offload point device, when a first air interface is unavailable, connection context information corresponding to service(s) of a user equipment on the first air interface, wherein the user equipment is connected to a core network through a first access network via the first air interface, and the user equipment is further connected to the core network through a second access network via a second air interface; the method being characterized by further comprising sending, by the offload point device via the second air interface, a first message to the user equipment, wherein the first message carries updating information related to the updated connection context information, and the updating information is used by the user equipment to update connection context information currently corresponding to the service(s) on the first air interface; and performing, by the offload point device, data transmission with the user equipment according to the updated connection context information; wherein before the updating the connection context information corresponding to the service(s) of the user equipment on the first air interface, the method further comprises: receiving, by the offload point device, a second message via the second air interface that is generated and sent by the user equipment and used for indicating that the first air interface is unavailable, or receiving a second message that is generated and sent by an access device of the first air interface and used for indicating that the first air interface is unavailable; and determining, by the offload point device, that the first air interface is unavailable according to the second message; wherein the second message is application layer signaling encapsulated in a data packet, and a header of the data packet carries a predefined identity to indicate that the data packet carries application layer signaling. receiving, by the offload point device, a second message via the second air interface that is generated and sent by the user equipment and used for indicating that the first air interface is unavailable, or receiving a second message that is generated and sent by an access device of the first air interface and used for indicating that the first air interface is unavailable; and determining, by the offload point device, that the first air interface is unavailable according to the second message; wherein the second message is application layer signaling encapsulated in a data packet, and a header of the data packet carries a predefined identity to indicate that the data packet carries application layer signaling.