A jack for preventing a headphone from inputting double audio sources includes: an audio jack set including a left audio jack and a right audio jack, which are respectively provided on bottoms of a left earpiece and a right earpiece of a headphone and for connecting an audio connector. The left audio jack includes a first common grounding contact, a first conductive terminal and a second conductive terminal. The right audio jack includes a second common grounding contact, a third conductive terminal and a fourth conductive terminal. Two audio jacks are provided for users to select. Simple mechanical switches are additionally provided, which only allow one inputted audio signal to input to a left earpiece and a right earpiece of the headphone for playing audio, and thus are capable of preventing users from inputting two different audio sources to the headphone simultaneously.