The disclosure discloses a Generic Mapping Procedure (GMP) mapping method for an Optical channel Data Unit (ODU), including: caching low-level ODUk data to a memory according to the rate of low-level ODUk data stream; generating an adjustment byte in a mapping process and encoding the adjustment byte; generating read enable of the cached data by an algorithm according to the adjustment byte, reading the cached low-level ODUk data, and generating Optical channel Data Tributary Unit (ODTU) data according to the read data; and crossing a time slot of the ODTU data in multiple channels to that of a high-level ODU payload, and forming the data in the time slot of the high-level ODU payload and the encoded adjustment byte into a completed high-level ODU frame. The disclosure may further provide a GMP mapping apparatus for an ODU. According to a technical solution of the disclosure, the GMP mapping of the ODU can be implemented according to the dynamic change of a service rate.