The Mn-Zn ferrite powder compact is heated by microwave with a frequency of 2.45 GHz. This essay illustrates the micro-mechanism of the interaction between microwave field and dielectric, elucidates the mechanism of soft-magnetic ferrite electromagnetic loss in microwave field, and discusses the characteristics of Mn-Zn ferrite powder compact when heated by microwave, as well as some factors such as microwave field E, dielectric constant εr , permeability μi, etc, which influence the heating temperature. Mn-Zn ferrite is a magnetic mixed media, and the basic reason for Mn-Zn ferrite powder compacts can be heated in microwave field is that the microwave electromagnetic energy can convert into heat along with energy loss. The energy loss mainly includes dielectric loss and magnetic loss, and the main factors influence the energy loss are microwave electromagnetic field intensity and its frequency.In a particular microwave field (2.45 GHz), the power of the microwave is the main influence factor of the sintering temperature , when the power of microwave changes, it leads to the change of the heating sintering curve. The material influence factors of the energy loss for Mn-Zn ferrite are permittivity εr and permeability μi, both chang with temperature,and frequency.