The probability of positronium (Ps) formation in molecular substances is investigated from the viewpoint of radiation chemistry. A new conception so called as "radiation protective function" (F) is proposed. A correlative equation with both the probability of Psformation (I,3,) and radiation protective function was derived in "ideal binary systems" according to the competitive reaction mechanism in the spur:,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42648060&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42648062&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42648061&type=,where α,0, β,0, are the parameters indicating the relative rate of competitive reactions between e,+, and A,+, or B,+, with e,-, in the spur, K=α,0,+β,0,. Furthermore, on the authority of this correlative equation, it is made a quantitative fittings with the I,3, values for systems of n-heptane-positive hole scavenger (dioxane, trimethylamine, pyrrolidine) and for aqueous solutions of some anions(I,-, Br,-, Cl,-, S,2-, SCN,-, and F,-,). It is found that in systems containing positive hole scavenger pyrrolidine possesses a larger radiation protection comparing with dioxane and trimethylamine to n-heptane, and that for anion aqueous solutions the order of radiation protection of the anions to water is I,-,>,SCN,-,>,S,2-,>,Br,-,>,Cl,-,>,F,-,. In fact, F,-, have nothing of the protection for water.