A simplified method for calculating the composition of vinyl chloride—vinyl acetate copolymers has been proposed in this paper．The composition nomogram and the composi-tion distribution diagram of the copolymer containing 0.84—-0.96 mole fraction of vinyl chloride have been constructed．If strict uniformity in the composition of the copolymer ig not required，the copolymer containing 85—95％ vinyl chloride by weight may be manu-factured by the once-charge method．The simplified method may be extended to compute the composition of other copolymer systems with γ1>1，γ2M1 is the main component．