A new antithrombosis dialytic membrane with a hydrophilic-hydrophobic microphase structure was prepared by preirradiation grafting of beta-hydroxyethyl methacrylate (HEMA) and styrene (St) onto ethylene-vinyl acetate (EVA). The influence of some effects, such as preirradiation dose, dose rate, grafting reaction temperature, reaction time, and monomer component, on the degree of grafting was determined, and the properties of the grafted films were investigated. Compared with the conventional EVA-grafted hydrophilic monomer, the EVA films grafted with HEMA and St have superior antithrombogenicity; the antithrombogenicity and permeability of EVA-g-(HEMA-co-St) were 30 and 20 times higher than those of the ungrafted films, respectively, when the volume ratio (HEMA versus St) was about 7:3.