This article presents a theory about the growth mechanism of bubble-screw dislocation of nodular graphite. Normally speaking, the crystallizing procedure of most nodular graphite is as follows: firstly, graphite generates nuclei on bubbles and fills them (mainly in the way of screw dislocation) forming the complete nuclei of nodular graphite-graphite bubble nuclei. Then, graphite grows up in the way of screw dislocation. Two important conditions concerning the production of nodular graphite are: (a) there is a relatively big interfacial energy between ferro liquid and graphite, and the one between ferro liquid and graphite prismatic plane is bigger than that between ferro liquid and graphite basal plane; (b) there are a certain amount of micro-bubbles in the melt. This article presents a theory about the growth mechanism of bubble-screw dislocation of nodular graphite. Normally speaking, the crystallizing procedure of most nodular graphite is as follows: first, graphite generates nuclei on bubbles and fills them (mainly in the way of screw dislocation Then, graphite grows up in the way of screw dislocation. Two important conditions concerning the production of nodular graphite are: (a) there is a relatively big interfacial energy between ferro liquid and graphite, and the one between ferro liquid and graphite prismatic plane is bigger than that between ferro liquid and graphite basal plane; (b) there are a certain amount of micro-bubbles in the melt.