Compared to conventional heating methods, microwave processing can provide more rapid heating in a clean environment with low energy consumption. For microwave processing, accurate computations of spatial and temporal temperature changes are imperative to achieve basic understanding and control of heating processes. This is especially important for materials in which absorption of microwave energy is highly temperature dependent. Based on the Lambert's law and heat transfer equations, a detailed mathematic model for predicting temperature profiles of the heated zirconium oxide in a microwave high-temperature reactor is developed. The heating behavior of zirconium oxide in the microwave high-temperature reactor is numerical investigated by using finite difference time domain method. The numerical calculation results by Lambert's law approach are very close to measurement value. It indicates that the Lambert's law approach is a feasible simple method to simulate the heating behavior of processed material in tube-type microwave high-temperature reactor.