A data transmission method and a terminal device are provided. The method includes: in response to that a terminal device selects to perform a data transmission in an inactive state based on a preconfigured uplink resource, sending, by the terminal device, uplink information to a network device. The uplink information includes at least uplink data to be sent by the terminal device, or the uplink information includes at least the uplink data to be sent by the terminal device and identity information of the terminal device.