A method for data transmission includes that: a first primary network device receives measurement result information of a secondary network device, transmitted by a terminal device in a process of accessing the first primary network device, the measurement result information indicates link quality between the secondary network device and the terminal device; the first primary network device determines to establish a secondary connection between the secondary network device and the terminal device according to the link quality between the secondary network device and the terminal device; and the first primary network device establishes the secondary connection. Another method for data transmission performed by a terminal device, and a device for data transmission are also provided.