A data transmission method in FlexE includes: obtaining multiple data blocks sent by L FlexE clients, where L is greater than or equal to 1; and sending a data frame including the multiple data blocks to a physical-layer device, where a transmission rate of the data frame is N*100 Gbit/s, the data frame includes T data block groups, each of the T data block groups includes M continuous data block subgroups, each of the M continuous data block subgroups includes R*N continuous data blocks, the data frame further includes T overhead block groups, a tth overhead block group includes N continuous overhead blocks. According to the method, each data block subgroup in a data frame can include R*N data blocks, and each overhead block group can include N overhead blocks, and a data transmission rate can be adjusted flexibly.