The waste fluorgypsum was modified and its comprehensive utilization with fly ash in concrete was studied. Eight-channel micro-calorimeter (TAM Air) and scanning electron microscopy were employed to study the basic properties and application performance of the modified fluorgypsum. Experimental results indicated that the modifying made the fluorgypsum crystal staggered mutually and improved the strength of the hardened body. The modified fluorgypsum and fly ash could delay reaction of cement hydration and reduce the heat of hydration of cement. When fluorgypsum was added to the cement, the fluorgypsum beared the function of enhancing the early stage compressive strength of concrete.