A numeric model was developed to couple electromagnetic (EM) and thermal field calculations in packaged foods moving in pressurized 915 MHz microwave (MW) cavities with circulating water at above 120 degrees C. This model employed a commercial EM package with a customized heat transfer sub-model to solve EM field and thermal field equations. Both methods applied finite-difference time-domain (FDTD) method. An interface was built to facilitate the communication between electromagnetic and thermal models to incorporate the coupling feature which is unique to microwave heating process. Special numerical strategies were implemented to simulate the movement of food packages. The simulation model was validated with a pilot-scale microwave system using direct temperature measurement data and indirect color patterns in whey protein gels via formation of the thermally induced chemical marker M-2. Good agreements were observed. Four cases were studied to investigate the influence of power input and package gaps on heating uniformity. These applications demonstrated the flexibility of the model to allow its usage for system and process optimization. (C) 2008 Elsevier Ltd. All rights reserved.