Chlorite is an important alteration in Mianhuakeng uranium deposit. The mineralogical characteristics of chlorite suggested that there were four main occurrence forms. The chemical composition of chlorite was studied by electron probe analysis. The results showed that chlorite was mainly iron rich peristaltic chlorite and ferromagnesium chlorite, which formed in the reduction environment. The chlorite of different origin and occurrence mostly comes from argillaceous rock, a few chlorite comes from magnesite, and the formation temperature of chlorite was between 187 ℃ and 297 ℃, Dissolution precipitation crystallization and dissolution migration precipitation crystallization are two important mechanisms of chloritization. In addition, chlorite is a Fe-rich layered silicate mineral, which provides a good reducing environment for uranium precipitation and enrichment in fluids.