A transient global model was used to obtain the solution of a thermal field within the entire furnace of a unidirectional solidification process. The melt-solid interface shape was obtained by a dynamic interface tracking method. Then, based on the global solution of heat transfer, the effects of growth rate Vg, temperature gradient G and ratio Vg/G on point defects were analyzed. Finally, several different melt-solid interface shapes were obtained by using different solidification times. Then the effects of solidification time on ratio Vg/G and point defects were also studied.