Raw coal was ground in a Hardgrove mill, and mineral liberation from coal was investigated by float-sink test and electron probe microanalyzer (EPMA). Based on EPMA, associated conditions of mineral were determined. Analyses of energy-size reduction show that energy efficiency decreases with time. For +0.074 mm progenies, yields of particles in -1.5 g.cm(-3) decrease with the increase of size and time, and products in +1.8 g.cm(-3) show the opposite trend. EPMA of 0.25-0.125 mm, 1.5-1.8 g.cm(-3) products ground for 10 min indicates that only part of minerals are liberated. For -0.074 mm products, the yield of particles in -1.5 g.cm(-3) decreases by 23.36% in last several minutes, but ash content of +1.8 g.cm(-3) also decreases by 13.18%. Since breakage of raw coal in last 9 min does not reduce particle size obviously, and liberation degree cannot be improved dramatically, closed grinding of 10 min in Hardgrove mill is proper to balance the size reduction and mineral liberation.