The invention relates to a method for hiding a personal data in an MP3 file, which involves an MP3 file A and a personal data B, and is characterized by being implemented by the following steps: decoding the MP3 file A into a pcm data flow by using an MP3 decoding program; and filling the personal data B in a space occupied by padding bits in a main information area, and adding a string of randomdigits to complete the coding after the completion of the filling. The method avoids increasing the MP3 file and generating obvious noises. The data flow can be image information, password information or another audio flow. The method has the advantages of novel design and high use value.