In this paper, the relationship between Tm and composition of PEO/PVAc blend were studied and the Flory-Huggins parameter of the blend system were calculated. The experimental results show that this blend system is compatible and have only one glass transition temperature (Tg), so we can extend the relationship between sol fraction (S) and radiation dose (R) of linear polymer to the PEO/PVAc system. The Bb value of PEO/PVAc system were calculated, which is in good agreement with the experimental value.