In this paper, the phase of electromagnetic field distribution in the cavity is regulated through movements of the metal wall of a rectangular waveguide, which can avoid the inhomogeneous heating caused by the uneven distribution of electromagnetic field in the rectangular waveguide. And the time varying medium method based on space coordinate transformation is proposed to calculate the moving boundary problem, which has a significant effect on solving the moving boundary problem of large industrial microwave cavities. A single mode BJ-22 wave guide heating system is used as the reference in this paper to analyze impacts of short circuit plane position on microwave heating uniformity. Experiments and calculation results show that the uniformity of microwave heating can be greatly improved by regulating of short circuit plane position, and the space coordinate transformation method can be used to calculate the moving boundary of the microwave cavity.
