The present invention provides a medium playing device for playing the media source and the related method. The method for playing a media source includes: extracting a reference subtitle stream from the media source, the reference subtitle stream being synchronized with a multimedia data stream of the media source; matching the reference subtitle stream to a substitute subtitle stream from a subtitle source for generating an output subtitle stream; and playing the multimedia data stream and the output subtitle stream synchronously. The medium playing device which plays the media source includes the following components: a demultiplexer, a caption engine and a mixer. As the method and the device which are provided by the invention for playing the media source can choose the desired caption document in another set, the selectivity of the system can be increased and the playing media source device can be adapted for more users.