This paper theoretically explores mediated negotiation as the practice of media diplomacy in resolving international disputes. It further discusses a mediated negotiation case, which is how U.S. and Russia made use of their own media to achieve mediated dialogue in the 2013 Syrian chemical weapons incident, by means of media frame interaction, source and metaphor analysis. It finds that the active-passive status of Russian and U.S. media in this incident affects the international public opinion and finally pushes forward the two countries to adopt Russia’s proposal to reach an agreement. This paper also discusses the mediated negotiation model consisted of frame interaction, source and metaphor, with the frame interaction to show the picture of the mediated negotiation, dialogue and discussion on core metaphors as the logic line throughout the whole process of mediated negotiation, and multiple sources to demonstrate one’s credibility and views.