Abstract: in order to study the gas ocurence law and dynamic disaster features of the coal seam undemneath the magmaic sil cover.the theoreical analysis andengineering case verfication method were aplid to analyze the seam metamorphic degreepore structure gas adsoption and desoptio perormances and gas ocurence features under the condtion of the magmatic ill cover. The control mechanism of gas dynamic disasters on th underlying cal seams by ill cover was revealedThe studyresults showed that the coal seam metamorphic degree pore stucture development degre and gas adsoption and desoption would have a closed relationship with the thickness and space distance of the magmati il cover.Generally they would be increased with the thickness of the illincreased and they would be decrased with the increasing ofth sil space distance with coal seams.Th ill ～ould applythe cap rock to soundlyseal the seam gas.thus.thesean gas pressure and gascontent would be increased.A coal and gas outburst disaster would be eaily occured under the mining or excavating and a well lowout and othr compicated gas oynamic disaster accidents would be occurred.