Provided in the embodiments of the present application are a method, a terminal device and a network device for data transmission. The method comprises: transmitting, by a terminal device, a first control signaling to a network device, wherein the first control signaling instructs the network device to allocate an uplink resource to first uplink data which are buffered and a backup uplink resource to the terminal device; receiving, by the terminal device, a second control signaling transmitted by the network device, wherein the second control signaling indicates the uplink resource allocated to the first uplink data and the backup uplink resource; transmitting, by the terminal device, the first uplink data on the uplink resource allocated to the first uplink data; transmitting, by the terminal device, second uplink data to the network device on the backup uplink resource if the second uplink data are buffered in the terminal device.