Abstract: Based on the characteristics of small cracks and large sample size of granular coal, the gas-bearing granular coal is taken as the research object, and the relationship between coal mechanical strength and gas is studied by using the firmness coefficient measuring device. The results of the study indicate that both adsorbed and free gas have a weakening effect on the strength of the coal body; the firmness coefficient of the coal containing adsorbed and non-adsorbed gas is approximately linearly negatively correlated with the gas equilibrium pressure; the effect of adsorbed gas on the firmness coefficient of coal is not obviously higher than that of free gas, but it tends to increase with the increase of adsorption equilibrium pressure; the change of firmness coefficient caused by the adsorption of coal gas is approximately linearly positive correlated with the adsorption amount, and the change of coal strength caused by the adsorbed state gas in coal can be predicted by the adsorption amount.