An uplink data transmission method, applied to a user equipment, wherein the user equipment establishes protocol stack layers corresponding to a first transmission branch and a second transmission branch of a split bearer, the protocol stack layers comprise at least a PDCP layer, an RLC layer, and a MAC layer, and the method comprises: starting a timer when a first operation is performed on first data on the first transmission branch, wherein the first data is data that has been transmitted to the RLC layer and/or the MAC layer of the first transmission branch and wherein the performing the first operation on the first data on the first transmission branch comprises: starting transmission of the first data on the first transmission branch, or completing transmission of the first data on the first transmission branch, or completing transmission of a part of the first data on the first transmission branch; and when timing of the timer ends, if a second operation is not performed on second data on the second transmission branch, performing a third operation on the second data, wherein the second data is data that has been transmitted to the RLC layer and/or the MAC layer of the second transmission branch, wherein if the second operation is not performed on the second data on the second transmission branch comprises: transmission of the second data is not completed on the second transmission branch, or transmission of the second data is not started on the second transmission branch, or transmission of a part of the second data is not completed on the second transmission branch, and wherein the performing a third operation on the second data comprises: canceling transmission of the second data; or deleting the second data; or canceling transmission of a part of the second data that has not yet been transmitted; or deleting the part of the second data that has not yet been transmitted; wherein after the performing the third operation on the second data, the method further comprises: transmitting a backup of the second data to the first transmission branch, wherein the backup of the second data is transmitted to a lower protocol stack layer of the first transmission branch and the backup of the second data is second data stored in a cache at the PDCP layer. starting a timer when a first operation is performed on first data on the first transmission branch, wherein the first data is data that has been transmitted to the RLC layer and/or the MAC layer of the first transmission branch and wherein the performing the first operation on the first data on the first transmission branch comprises: starting transmission of the first data on the first transmission branch, or completing transmission of the first data on the first transmission branch, or completing transmission of a part of the first data on the first transmission branch; and when timing of the timer ends, if a second operation is not performed on second data on the second transmission branch, performing a third operation on the second data, wherein the second data is data that has been transmitted to the RLC layer and/or the MAC layer of the second transmission branch, wherein if the second operation is not performed on the second data on the second transmission branch comprises: transmission of the second data is not completed on the second transmission branch, or transmission of the second data is not started on the second transmission branch, or transmission of a part of the second data is not completed on the second transmission branch, and wherein the performing a third operation on the second data comprises: canceling transmission of the second data; or deleting the second data; or canceling transmission of a part of the second data that has not yet been transmitted; or deleting the part of the second data that has not yet been transmitted; wherein after the performing the third operation on the second data, the method further comprises: transmitting a backup of the second data to the first transmission branch, wherein the backup of the second data is transmitted to a lower protocol stack layer of the first transmission branch and the backup of the second data is second data stored in a cache at the PDCP layer. canceling transmission of the second data; or deleting the second data; or canceling transmission of a part of the second data that has not yet been transmitted; or deleting the part of the second data that has not yet been transmitted; wherein after the performing the third operation on the second data, the method further comprises: transmitting a backup of the second data to the first transmission branch, wherein the backup of the second data is transmitted to a lower protocol stack layer of the first transmission branch and the backup of the second data is second data stored in a cache at the PDCP layer.