This paper introduces and analyses a novel dielectric base plate with an asymmetric shape and dielectric property aiming to achieve a uniform temperature distribution over the heating sample. Firstly, the proposed dielectric base contains FR-4(FR-4 Epoxy Glass Cloth) and alumine and is located within a commercial microwave oven to heat a potato sample. The permittivity and geometric values of the base are the selected parameters to be optimized for the sake of lowering the Coefficient Of Variation(COV) of temperature on the spherical medium heating sample and improving heating uniformity. Secondly, calculation of the multiphysical field simulation is applied to simulate the heating process. The simulation results based on COMSOL Multiphysics show that the COV decreases from 0.9134 to 0.5446 with the dielectric base. In other words, the COV declines by over 40%. Finally, an experimental system is built to measure the temperature of the heating sample to validate the simulations and calculations. Good agreements have achieved between the simulation and experiment, showing good consistence in temperature rise curves. It illustrates that the novel dielectric base can make the temperature uniformity of the heating sample improved.