Media diplomacy has been frequently discussed in the past few years, yet scholars have not agreed on what media diplomacy is. This paper tries to clarify the relationship among diplomacy, public diplomacy and media diplomacy based on the mechanism of communication firstly. After analyzing the interpretations of media diplomacy brought up by the scholars both home and abroad, it tries to analyze the dimensions and analytical factors of media diplomacy. It finally gives an operational definition of media diplomacy, aiming to outline the layers and communication factors of media diplomacy and set up the research framework of media diplomacy.