The content of calcic minerals in fly ash is an important factor affecting the properties and application of fly ash. We reviewed information about and analyzed the formation of calcic minerals in fly ash and the negative effects of calcic minerals on fly ash properties. We found that the content of SO3 versus CaO is a linear relationship. Fly ash morphology and degree of silicate polymerization vary as the calcic minerals content in fly ash increases. Higher levels of calcic minerals in fly ash may cause poor soundness of cement and concrete added with fly ash; high content calcic minerals in fly ash may become an advantage, however, when the volume of fly ash used in concrete is limited and the fly ash is pretreated.