A data transmission method, a terminal, and a network device are provided. In embodiments of the present disclosure, a terminal sends, in a grant-free mode, first data to a network device by using a grant-free resource, and if the terminal needs to switch from the grant-free mode to a grant mode, the terminal sends, in the grant mode, second data to the network device by using a grant resource. When the terminal initially transmits the first data in the grant-free mode, if the terminal needs to switch from the grant-free mode to the grant mode, the terminal may fall back to the grant mode and transmit data in the grant mode.