The temperature-field in diamond synthesis cell was simulated by a finite element method. A three-dimensional model of the China-type cubic press with large deformation of the synthesis cell was established successfully, which has been verified by situ measurements of synthesis cell. In addition, the distributions of temperature and its gradient in the synthesis sample were described. We found there is a large temperature drop in the synthesis sample, which brings some uncertainties in a synthesis process, such as the phenomenon of "wasteland, on which there is no nucleation and growth of diamond". Furthermore, the formation mechanism of wasteland was studied in detail. It indicates that the wasteland is inevitably exists in the synthesis sample, the distribution of growth region of the diamond with hex-octahedral is move to the center of the synthesis sample from near the heater as the power increasing, and the growth conditions of high quality diamond is locate at the center of the synthesis sample. This work can offer suggestion and advice to the development and optimization of a diamond production process. (C) 2015 Elsevier B.V. All rights reserved.