In order to clarify the effect of antimony on graphite morphology and mechanical properties in heavy section ductile iron, experiments were carried out using a newly developed thermal simulation system. Results show that with 0.011% addition of antimony, tensile strength of heavy section ductile iron are obviously improved by elimination of graphite degeneration in it, and the effect of antimony is increased when the addition is increased to 0.02%. In the range of 0.01 similar to 0.04%, antimony is beneficial to graphite morphology and tensile strength although the advantageous effect on them become not so obvious when addition is exceed 0.02%.