In this article, the influence of the flow field structure and temperature gradient of forefront interface on the shape of crystal melt interface which may reflect the interface stability were analyzed through the method of numerical simulation by using CGSim software. In order to get a suitable interface shape and grow high quality sapphire crystal, the heater arrangement should be adjusted during the KY process. The results indicate that the effect of Marangoni convection cannot be neglected at the last stage, the crystal melt interface is governed by the flow field structure and the temperature gradient in melt at the crystal melt interface. The phenomenon of shoulder concave appears at the stage of shoulder turning and interface inversion appears at the last stage during the crystal growth is discussed. Adjusting heater arrangement may effectively optimize the shape of crystal melt interface. (C) 2015 Elsevier BM. All rights reserved.