Start from the Adler-Bardeen relation and have derived a formula of the quark content of the proton spin, when the π - η - η′ mixing and the higher order correction of the isospin breaking is considered. 从Adler-bardeen关系出发,并考虑到同位旋破缺的高阶修正和π-η-η′混合,推出了夸克对质子自旋的公式。