CdZnTe is one of the most concerned materials for nuclear radiation detection in room temperature semiconductor and traveling heater method (THM) is one of the most promising methods for single crystal CdZnTe growth. The interface stability has a great influence on the quality of CdZnTe crystals grown by THM. In this paper, based on the multi-physical field finite element simulation software Comsol, the numerical simulation model of CdZnTe crystal grown by THM was established. The concept of Te boundary layer was explained, and the relationship between Te boundary layer and constitutional supercooling zone was proposed. The physical field at different growth stages was simulated. The variations of constitutional supercooling zone and Te boundary layer at different stages of growth were analyzed. Finally, the effect of microgravity on physical field of THM was discussed. In order to study the stability of the growth interface, the morphology of growth interface under microgravity and normal gravity was compared. Simulation results show that the distribution of Te boundary layer is consistent with the constitutional supercooling zone. The simulation shows that the secondary vortex which is caused by the inverse temperature gradient at the growth interface front appears. The position of secondary vortex in the flow field of THM changes at different growth stages which leads to the change of growth interface as the growth proceeds. A slight convex or flat growth interface forms when the secondary vortex appears near the crucible wall. Considering the condition of microgravity, a convex growth interface will be formed which is beneficial to the growth of CdZnTe single crystal. Therefore, the control of secondary vortex and decrease of supercooling during the THM growth is an effective scheme for the growth of high-quality CdZnTe crystals under mormal gravity condition.