With the increasing deepening of the study on crystallization mechanism of the magmatic system the magmatic kinetic theory of volcanic and intrusive rocks has entered the stage of establishing a model. Through the study of the example of Shaxi porphyry body in Anhui Province the authors first figured out the storage time of plagioclase phenocrysts} then calcufated the nucleation rate and growth rate of the crystals and，on such a basis established the thermal model for cooling of the hypabyssal magmatic system.