Abstract: In order to determine the influence of different experimental temperature on coal firmness coefficient, we designed and manufactured the test device with adjustable temperature, determined firmness coefficient of different coal samples from -20 ℃ to 60 ℃ in every 10 ℃. Experimental results show that coal firmness coefficient decreases with the temperature increase, and increases with the decrease of temperature; the influence degree of coal samples is different under different temperature; the harder the coal body, the greater the amplitude; the soft the coal, the smaller the amplitude.