This paper presents two-dimensional numerical analysis of heat-mass transport and pressure buildup inside an unsaturated porous packed bed which is filled in a rectangular waveguide and subjected to a combined microwave and vacuum system. A microwave system supplies a monochromatic wave in a fundamental TE10 mode. The unsaturated porous media is composed of glass beads, water and air. The finite difference time domain method is used to determine the electromagnetic field distribution in the rectangular waveguide by solving the transient Maxwell's equations. The finite difference method together with Newton-Rephson technique is employed to predict the heat, multiphase flow and pressure buildup. The influences of vacuum pressure and operating microwave frequency on temperature, microwave power absorbed, saturation and pressure buildup distribution, and movement of fluid inside the unsaturated porous media are investigated during microwave vacuum drying process. (C) 2013 Elsevier Ltd. All rights reserved.