The invention discloses a method for a communication terminal with a USB sound card and a method used for realizing the USB sound card in the communication terminal. The communication terminal comprises a central processing unit and an analog baseband processor which are interlinked with each other. The central processing unit comprises a USB terminal controller and an I2S bus controller which is connected with the USB terminal controller and supports bidirectional I2S bus data format conversion. The analog baseband processor is internally provided with an audio frequency codec which is used for coding and decoding audio frequency data. The USB terminal controller, the I2S bus controller and the audio frequency codec are multiplexed to form the USB sound card. In the invention, partial functions of the central processing unit and the analog baseband processor in the communication terminal are multiplexed, so as to realize the USB sound card based on I2S bus, and the USB sound card can match and use the functions of multimedia such as MP3, MP4 and the like in the communication terminal, so as to ensure that the communication terminal has the application value of the multimedia furthermore.