This paper focuses on the influence of various design parameters on microwave heating performance by coupling of the electromagnetic and the heat transfer equations by COMSOL Multiphysics software. The coupled model of microwave heating is numerically implemented using a finite element method and validated by comparison with previous experimental results. Results indicate that samples with different permittivities show different temperature rise. With some design parametric variations such as cavity shape, waveguide location, loading sample position and so on, the heating effects which are the energy utilization and temperature distribution exhibit sensitively. The results show that with the waveguide location changing with axial direction of cavity, the heating performance will fluctuate not monotonically while repeating, which means the optimal waveguide location is not unique. Furthermore, when the loading samples situate off the center of cavity, the heating effect is even better. Since previous studies barely paid attention to the structure design of cavity and inside vessel, this work concentrates on specific cavity and heating equipment which in turn fills design rules of microwave heating process and offers guidance for the design and scaling-up of microwave applicator. (C) 2019 Elsevier Ltd. All rights reserved.