The invention relates to a method and a device for playing an online audio/video by a mobile terminal. The method comprises the following steps: firstly, dividing a buffer area of the mobile terminal into two areas; secondly, downloading audio/video data and storing the audio/video data in the two areas; thirdly, playing the audio/video data according to a storing sequence, clearing one area when the audio/video data in the area finishes and continuously downloading audio/video data to the area. The device comprises a dividing unit, a downloading and storing unit, a playing unit and a processing unit. In the invention, by dividing the buffer area into two areas, the audio/video data can be played and continuously download at the same time, and the play of the audio/video data can not be influenced while clearing the buffer area, thereby the efficiency of downloading and the using experience of the user are both improved.