Abstract: Following results were obtained in present work by using thermal and structural methods: 1.Graphite spheroid was formed directly from liquid phase, and was grown independently keeping complete spheres when modification was optimum. In hypereutectic cast iron austenite was formed only during eutectic trasformation and primarily was grown on the surface of the graphite sphere. 2.When modification was not optimum the graphite spheres (being on the stage of free growth) distorted themeslf when there were not any other solid phases. 3.In the low S iron melt which didn't have modification the graphite was formed at first in the shape of small spheres (3-5micron), and then the graphite grows "horn" on it's surface. This phenomenon became stronger in consequence of the increase of S, and the graphite grows in the shape of "paw". By using oversaturated formation method it was found on the graphite surface the appearance of screw crystal and it's steps. The graphite which had been modificated kept spheroidal in shape and on it's surface screw crystals with different orientations could been seen. By using thermal and structural methods this work discovered that in hypoeutectic iron which was in non-equilibrium state the graphite spheres were formed from the hypereutectic liquid phase. The non-equilibrium state was caused by modification and inoculation. By putting in the silicon and using local-spectroscopic analysis determined the occurrence of local fluctuation of compositions. On the basis of the analysis of the experimental results the author proposed the models of the embryo and of the growth of the graphite during primary crystallization of cast iron. In this paper the author expressed his opinions on effect of the sphericized elements and the anti-sphericized elements and propounded the mechanism of inoculation.