Abstract: In order to analyze the variation law of the seam gas permeability occurred in the rising and dropping of the in-situ rock stress under the influences of th e mining operation, the MYS-I permeability measuring system of coal and rock sample was applied to the comparison study on the permeability difference between the briquette coal sample and the raw coal sample with the method to change the surrounding pressure and the gas pressure.The test results showed that there was a big difference of the permeabllity between the briquette coal sample and the raw coal sample and there was about a quantitative order difference in the numerical value.Un der the condition of the fixed gas pressure, the permeability of the raw coal sample would be reduced with the surrounding rock pressure increased, but the reduction s peed would be slower than the briquette coal sample.The permeability of the briquette coal sample and the raw coal sample would have the same variation tendency wit h the surrounding rock pressure and the gas pressure changed.In the lab, the briquette coal sample would be feasible to replace the raw coal sample for the permeabilit y test, but would be only for the study of the general variation law.