Abstract: Many microwave reactors widely used in laboratory are made from commercial microwave ovensIn this paper, the heating process inside the reactor was simulated in order to obtain the final temperature distribution in the solution in a beakerMaxwell’s equations and the heat transport equation (HTE) were coupled to calculate the temperature results by means of the finite element method (FEM).In the calculation, Debye’s equation and Huang’s method were used to describe the temperature and time dependence of dielectric propertiesDue to the non-uniform distribution of fields in the cavity, the heating results varied significantly with the position of the beakerThis could be more obvious for a chemical reaction because of the non-equilibrium characteristicsIt was also observed that the repeatability of experiments was poor even for a fixed position of the beaker due to the magnetron instabilityTherefore, such chemical reactors made from commercial microwave ovens can hardly ensure the repeatability of experiments.observed that the repeatability of experiments is poor even for a fixed position due to the magnetron’s instability. Therefore, such chemical reactors made from commercial microwave ovens can hardly ensure the repeatability of experiments.