Abstract In situ investigation of the microstructure evolution and the mixed-interaction mechanisms of metal–ceramic materials during the microwave sintering process was carried out using the synchrotron radiation computed tomography technique. The results indicate that there are some special mixed-interaction mechanisms, which may promote the sintering process during the microwave heating of metal–ceramic materials. In the experiment, some particular sintering phenomena that differ from the microwave sintering of pure metal materials were observed, such as fast interface bonding and particle swallowing. Quantitative analysis of the microstructure evolution during microwave sintering showed that the decrement of grain surface bending energy of metal–ceramic materials was slower, while the sintering-neck growth rate was higher than that of the pure metal materials. These results may be caused by the mixed-interaction mechanisms between microwave and metal–ceramic materials, such as the “micro-focusing effect”, the special microwave interaction mechanisms on the particle surface and the heterogeneous metal–ceramic interface. This study will help to provide a useful reference for the improvement of the microstructure characteristics of metal–ceramic materials in microwave sintering.