Calcined coal gangue (CCG) exhibits promising application potential in limestone-cement binary binders. However, the activity of CCG would possibly be weakened due to the particle agglomeration after calcination. In the present research, we tried to overcome this challenge by ball-milling and investigated the effect of ball-milled CCG on the hydration of blended cement with limestone. The ball-milled CCG was firstly analyzed concerning particle size distribution, morphology and mineralogical composition. Then the influence of the ball-milled CCG on the workability, hydration, hydrates and pore structures of the blended cement with limestone was also assessed. The results revealed that ball-milling effectively decreased the average particle size of CCG with a narrower particle size distribution, whereas did not significantly alter its chemical and mineralogical compositions. The ball-milled CCG effectively improved the compressive strength of CCG-prepared mortar from 3 d onwards, and the corresponding 28-day compressive strength was even 3.1 %-7.1 % higher than that of the reference Portland cement (PC) mortar. The ball-milled CCG was conducive to precipitating more hydrates and benefiting to the porosity refinement, well supporting the compressive strength development. With considering electricity consumption and compressive strength, 30 min of ball-milling appears to be an optimal duration. The findings of this research provided a novel way to promote the efficient utilization of CG in cement-based materials.