A data transmission method in an optical transport network includes: mapping first-type service data to a payload block at a specific location in a plurality of consecutive payload blocks, where the plurality of consecutive payload blocks occupy a payload area of an optical data unit (ODU) frame; mapping second-type service data to a payload block at any location in the plurality of consecutive payload blocks other than the at least one specific location; mapping the ODU frame to an optical transport unit (OTU) frame or a flexible OTN (FlexO) frame; and sending the OTU frame or the FlexO frame. In an applicable scenario, service data is transmitted in a hybrid manner.