An air flow system in oven is provided. The structure includes: a cavity for housing food; a ventilation fan provided at an electronic equipment chamber outside of the cavity; a first intake port provided at a front and upper surface of the microwave oven; a lower barrier for partitioning a lower space of the cavity; an outlet duct provided at one side of the lower barrier, for allowing a flow of hot air using the ventilation fan; an outlet space provided at the other side of the lower barrier, for exhausting an internal air of the cavity; a plurality of front outlet ports provided at a front and lower surface of the microwave oven, for exhausting hot air of the outlet duct and the outlet space; and a communication port provided at one side of the lower barrier, for communicating the outlet duct with the outlet space.