The present disclosure relates to operation, administration and maintenance (OAM) data transmission methods and apparatus. One example method includes obtaining a first data flow and sending the first data flow. The first data flow includes at least one first OAM data block. The at least one first OAM data block is a code block that carries first OAM data. The first data flow is a data flow obtained by deleting at least one redundant block or at least one second OAM data block from a second data flow and inserting the at least one first OAM data block, or the first data flow is a data flow obtained by modifying at least one second OAM data block in a second data flow. The second data flow is an aggregated data flow. The second OAM data block carries second OAM data.