Abstract: Using the self-made testing device of coal seepage and spontaneous combustion of compacted broken coal, the evolution characteristics and mechanism of bulking coefficient of broken coal under different conditions of stress, stress-temperature,and stress-water were tested and analyzed. The results show that:① the bulking co-efficient of bro- ken coal has obvious stage with the increase of stress,and the change rule of bulking coefficient under the stress meets with the negative exponent. ② under the same axial compression,the bulking coefficient increases with the increase of temperature,and the thermal expansion effect is obvious,which indicates that the thermal effect of spontaneous com- bustion will increase the bulking coefficient and loose the accumulation of broken coal in gob. ③ when the water con- tent increases in vitro of the broken coal,under the same axial com-pression,the bulking coefficient increases with the increase of external moisture,which shows that the broken coal bulking coefficient will increase with the increase of water. ④ under the action of stress,thermal expansion and wet expansion,the internal particles occur relatively moving in the accumulation body, secondary crushed and granular self-accumulation, which cause the stress-strain curve change,and the bulking coefficient affected.