A method includes determining, by a terminal device, a relation of size between an amount of data to be sent of a first split bearer of the terminal device and a preset threshold of the first split bearer, wherein the amount of the data to be sent includes a total amount of data volume in a PDCP layer of the first split bearer and an amount of data in a first RLC layer that is configured by a network side on the first split bearer and that is used to transmit data by default. The method also includes determining according to the relation of size in a plurality of cell groups corresponding to the first split bearer, a target cell group used to process the data to be sent according to the relation of size. The method facilitates load balance between cell groups and data transmission flexibility.