Abstract: To explore the relationship between firmness coefficient (f value) and porosity of coal, the firmness coefficient and porosity of different types of coal were tested respectively, and the comparison of the test results was made. The coal samples were excavated from Xin'an Coal Mine, Xindeng Coal Mine, Yanmazhuang Coal Mine and Linhuan Coal Mine. The results indicated that the relationship between firmness coefficient and porosity is positive correlated of the same type of coal; and the porosity, to varying degrees, increases with the increases of firmness coefficient of different types of coal; and there are no obvious change law between different types of coal that with bigger otherness.