Embodiments of this application relate to the field of optical communications, and in particular, to a technology of processing data in an optical transport network. In a method for processing data, an optical network device extracts Ethernet data from a data frame of one path, converts the Ethernet data into another format, and places the Ethernet data converted into the another format into a data frame of another path. The optical network device is a destination device of the path and a source device of the another path. In addition, the optical network device further extracts overhead information from the data frame of the path, and inserts the overhead information into the data frame of the another path. The method for processing data provided in this application can implement interworking between different types of Ethernet interfaces. In addition, by using cross-path overhead processing, the method reduces path management complexity.