By using X-ray diffraction (XRD) and environmental scanning electron microscope (SEM) analysis method, we studied the activity of coal gangue fine aggregate under different calcination temperature. In view of the activity of the highest 700 ℃ high temperature calcined coal gangue fine aggregate mortar of hydration products, microstructure and strength were discussed in this paper, and the change laws of mortar strength with curing age (3, 7, 14, 28, 60 and 90 d) growth were analyzed. Test results showed that coal gangue fine aggregate with the increase of calcination temperature, the active gradually increases. When the calcination temperature reaches 700 ℃, the activity of coal gangue fine aggregate is the highest. When calcining temperature continues to rise, activity falls. After 700 ℃ high temperature calcined coal gangue fine aggregate has obvious ash activity, the active components of SiO2 and Al2O3 can be with cement hydration products in a certain degree of secondary hydration reaction. Through on the top of the activity of different curing age 700 ℃ high temperature calcined coal gangue fine aggregate mortar, XRD and SEM analysis showed that with the increase of curing age, secondary hydration reaction will be more fully, and the amount of hydration products also gradually increases. Compared with the early ages of the cement mortar, the products are more stable hydration products filling in mortar microscopic pore, which can further improve the microstructure of mortar, strengthen the interface performance of the mortar. The mortar internal structure is more uniform, calcined coal gangue fine aggregate and cement mortar are more of a strong continuous whole, which increase the later strength of hardened cement mortar, 700 ℃ high temperature calcined coal gangue fine aggregate pozzolanic effect is obvious.