1. A system for obtaining user-selected audio key phrase from a series of audio contents, comprising: an output module outputting the audio contents to a user, wherein the audio contents include a plurality of audio phrases and audio key phrases, wherein the plurality of audio key phrases are highlighted by one selected from the group consisting of a play speed, a tone, a sound volume, and a combination thereof; an input module receiving a speech input from the user, wherein the speech input includes the user-selected audio key phrase based on the audio contents being output; a buffer temporarily storing a number of outputted audio key phrases within a desired period and the speech input, wherein the desired period is a prior period of time before a moment when the speech input is received by the input module; and a recognizing module performing a speech recognition by matching the number of the outputted audio key phrases during the desired period with the speech input, so as to obtain the user-selected audio key phrase.