Abstract: In this paper, mineral composition , physico-mechanical properties, physico-chemical parameters, cement materials and microstructure of three typical mudstones from Shigu coal mine in Guangdong province measured are analysed in this paper, and from the point of view of physico-chemistry and mechanics, the effect of water quality change, loss of water content and microstructureal damage on swelling of mudstone is investigated, The result indicates that the clay mineral of mudstone mainly consists of kaolinite and elite, its swelling pressure is 2~5kg/cm2 and induced swelling pressure and the effect of swelling capacity on physico-chemical and mechanical factors are attributable to high clay content, fine clay aggregate, poor crystal, rarely cement materials and dense microstructure.