A method for establishing a secondary connection, comprising: acquiring, by a primary access network device, secondary network access capability information of a terminal device, wherein the secondary network access capability information is used to indicate a capability for the terminal device to access a secondary access network device; sending, by the primary access network device, a secondary connection addition request message to a first secondary access network device, wherein the secondary connection addition request message is used to request addition of the first secondary access network device as a network device for transmitting data, and the secondary connection addition request message comprises the secondary network access capability information; and receiving, by the primary access network device, a confirmation message of the secondary connection addition request message sent by the first secondary access network device, wherein the confirmation message of the secondary connection addition request message comprises first configuration information; sending, by the primary access network device, the first configuration information to the terminal device so that the terminal device establishes the secondary connection with the first secondary access network device according to the first configuration information; wherein before the sending, by the primary access network device, the secondary connection addition request message to the first secondary access network device, the method comprises: receiving, by the primary access network device, measurement result information of at least one secondary access network device sent by the terminal device, wherein the measurement result information is used to indicate a link quality between a respective secondary access network device and the terminal device; and determining, by the primary access network device, the first secondary access network device according to measurement result information of each of the at least one secondary access network device; wherein the secondary connection addition request message further comprises second configuration information, wherein the second configuration information is configuration information of a secondary connection that has been established by the terminal device. acquiring, by a primary access network device, secondary network access capability information of a terminal device, wherein the secondary network access capability information is used to indicate a capability for the terminal device to access a secondary access network device; sending, by the primary access network device, a secondary connection addition request message to a first secondary access network device, wherein the secondary connection addition request message is used to request addition of the first secondary access network device as a network device for transmitting data, and the secondary connection addition request message comprises the secondary network access capability information; and receiving, by the primary access network device, a confirmation message of the secondary connection addition request message sent by the first secondary access network device, wherein the confirmation message of the secondary connection addition request message comprises first configuration information; sending, by the primary access network device, the first configuration information to the terminal device so that the terminal device establishes the secondary connection with the first secondary access network device according to the first configuration information; wherein before the sending, by the primary access network device, the secondary connection addition request message to the first secondary access network device, the method comprises: receiving, by the primary access network device, measurement result information of at least one secondary access network device sent by the terminal device, wherein the measurement result information is used to indicate a link quality between a respective secondary access network device and the terminal device; and determining, by the primary access network device, the first secondary access network device according to measurement result information of each of the at least one secondary access network device; wherein the secondary connection addition request message further comprises second configuration information, wherein the second configuration information is configuration information of a secondary connection that has been established by the terminal device. receiving, by the primary access network device, measurement result information of at least one secondary access network device sent by the terminal device, wherein the measurement result information is used to indicate a link quality between a respective secondary access network device and the terminal device; and determining, by the primary access network device, the first secondary access network device according to measurement result information of each of the at least one secondary access network device; wherein the secondary connection addition request message further comprises second configuration information, wherein the second configuration information is configuration information of a secondary connection that has been established by the terminal device.