The present invention relates to the field of communications network technologies, and discloses a data processing method and apparatus. In embodiments of the present invention, stream channel quality information is obtained, and then port mapping of a to-be-transmitted data stream is determined according to the stream channel quality information. The port mapping is used to make channel quality of data streams distributed in a same code word satisfy the following: a sum of fluctuation values that is used to represent channel quality of data streams in all code words is less than a sum of fluctuation values that is used to represent channel quality of data streams in all code words under original port mapping.