The utility model relates to a microwave resonant cavity comprising a microwave resonant cavity and a light reflection surface arranged at the top surface inside the resonant cavity. The light reflection surface is provided with two microwave energy feeding openings. Two opposite sidewalls of the microwave resonant cavity are provided with a plurality of air vents. The air vents on one side are an air-inlet side. The air vents on the other one side are an air-outlet side. The high-heat radiation-type microwave resonant cavity of the utility model is simple in structure and easy to manufacture. A microwave guiding cavity and a microwave resonant cavity which are of a split structure are adopted. The microwave resonant cavity is design individually, and the microwave resonant cavity and the light reflection surface are manufactured through one-body or casting. The production, the assembly and the maintenance are provided with convenience. The microwave resonant cavity employs a one-body structure, so that heat of other parts of a microwave ultraviolet light source isolated and is prevented from entering the microwave guiding cavity, and the processing of a lot of materials with low poor resistance properties become possible. Air in the front end of the microwave resonant cavity moves in a horizontal direction, so that the cooling efficiency is raised.