Abstract: In order to optimize the determination method of the roof bulk increase coefficient under the condition of gob-side entry retaining formed by roof cutting and further explore its evolution law, the present calculating methods are summarized at first. Then based on the compound roof of 8304 working face in Tashan Coal Mine, through detailed geological examination, natural observation, marker observation and layer thickness calculation, getting the bulk increase coefficient of roof is about 1.40. And the field measurement shows that the lumpiness of the mudstone is smaller than the fine sandstones’, but the bulk increase coefficient is bigger and the length of the coefficient stability zone is longer. Besides, combined with the monitoring of gangue wall maintaining pressure, what can be seen is the lateral pressure of gangue wall decreases when the retaining entry is stable, but the bulking coefficient of gangue has no obvious rebound rise.