Abstract: For the investigation on microwave heating process, heating characteristics of straw bale under microwave heating were studied in this paper. Microwave heating was considered as an internal heat source, and Lambert's law was adopted to simplify the distribution of internal heat source. And then the temperature distribution of large-sized materials during microwave heating was calculated using a heat conduction differential equation with an internal heat source. Finally, the temperature distribution of straw bale during microwave heating was measured on a microwave heating device self-designed and constructed and compared with the simulation results. The comparison results show that numerical simulation results are basically able to reveal the heat transfer mechanisms during the microwave heating process and have a significant guidance to the utilization of microwave pyrolysis.