In grafting acrylonitril and styrene on ethylene vinylacetate copolymer, the morphological phase structure was studied in relation to the physical properties of the polymer thus produced. It was found that a certain amount of EVA-AS graftmer takes an important role on the stabilization of phase structure between EVA particle as rubber and AS continuous phase of plastic field. During the polymerization process, the phase inversion took place from EVA continuous phase to EVA particle. The phase structure of EVA particle in AS continuous phase is inevitable for increasing impact resistance property of the polymer, which is resulted in the necessity of increasing the graft efficiency of AS on EVA. Diacyl type initiator is not effective for increasing graft efficiency and peroxyester type initiator conducts much higher graft efficiency which leads to low melt index due to increasing of super-high molecular weight portion. Combination of the initiators mentioned above is effective from the practical point of view. The phase structure formulated by suspension polymerization is unstable because of the fact that the phase structure easily changes by roll-mixing. The sophisticated method of bulk-suspension polymerization implements the stability of the phase structure.