Abstract: On the basis of the tri-axial stress measurements, a gas-solid coupling tri-axial stress servo seepage experimental device is developed; taking the raw coal sample that the firmness coefficient f is less than 0.5 as the research object, the results show that the firmness coefficient of the soft tectonic coal in the range of 0.26 to 0.48 also experiences five stages in the process of stress and strain loading, however, when the coefficient of firmness is relatively small, it shows that the drop range of stress decreases or disappears gradually; the gas permeability of raw coal samples from the same mining area increases with the increase of the firmness coefficient, and in line with the quadratic polynomial K=af²+bf+c.