In this work, a mathematical model for stable and metastable transformation of SG cast iron, coupling with microsegregation of some elements and latent heat resulted from different phase formation, was presented. The quantitative experimental results of specimens obtained from a step-shape sample casting were compared with the simulation, and two results of nodular counts and sizes agreed quite well. For white eutectic growth in mottled SG iron, the frequent impingement of white eutectic with austenite-graphite bulks might suppress its growth remarkably and result in quite lower growth rate than that from the melt exclusively. Meanwhile, the relationship of morphology of carbides and solidification was discussed, and it was indicated that the growth of white eutectic and carbide morphology could also be predicted by solidification simulation. It was found that neglecting silicon microsegregation, if metastable transformation was advantageous to stable, the simulated carbide fraction was higher, and vice versa.