Embodiments of the present disclosure relate to a data transmission method, a terminal device and a network device. The method includes: receiving a downlink data packet transmitted by a network device, where the downlink data packet includes an RQI; determining a working mode of the RQI, where the working mode of the RQI is used to determine an indication content of the RQI, the indication content includes whether a first mapping relationship and/or a second mapping relationship satisfies a reflective QoS mapping; determining the first mapping relationship and the second mapping relationship of an uplink data packet according to the working mode of the RQI and the RQI. The terminal device may determine, according to the RQI of only 1-bit, whether the first mapping relationship and the second mapping relationship of the uplink data packet to be transmitted to the network device satisfy the reflective QoS.