Abstract: The mechanism of microwave interaction with substance was analyzed by means of Maxwell electromagnetic theory. The results showed that the microwave absorption
of substance was caused by the conductive loss and dielectric relaxation loss of substance, at high temperatures the conductive loss will be main loss. Heating
with 2.45GHz microwave, the substance conductivity must be lower than 1Ω^-1cm^-1. With the conductive data. The microwave heating charaeteristic of some inorganic
nonmetallic materials were evaluated. The temperature distribution within a sample was described with some hypothesis when microwave heating. The behavior of
nonhomogeneous solid under microwave irradiation was simply evaluated and predicted.

Key words: microwave heating, dielectric loss, inorganic nonmetallic substance