To study role of fault to mudstone caprock in oil-gas accumulation and presentation, based on the study of destroy mechanism of fault to mudstone caprock and its influence factors , a comprehensive quantitative research method of destroy degree of faults to mudstone caprock were established by the method contrasting between fault distance and thickness of mudstone caprock and contrasting between displacement pressure of fault rock and displacement pressure of mudstone caprock. Used faults in mudstone caprocks of 14 Volcanic gas reservoirs of k1yc in Xujiaweizi depression as an actual example ,their destroy degree to mudstone caprocks of 14 Volcanic gas reservoirs of k1yc in Xujiaweizi depression was studied comprehensively and quantitatively .The result indicate that destroy degree to mudstone caprocks of 14 Volcanic gas reservoirs of k1yc in Xujiaweizi depression was evaluated to be weak, destroy degree to mudstone caprock in only two gas reservoirs can get to stronger . It is favorable for gas to accumulate and preserve in gas reservoirs. It is one of the important cause that a lot of gas reservoirs have been found in Volcanic rock of K1yc in Xujiaweizi depression.This indicates that the method is practical to evaluate comprehensively and quantitatively destroy degree of faults to mudstone caprock.