Abstract: For problems that gas adsorption-desorption method for determining gas diffusion coefficient is limited to coal particle and cannot apply confining pressure and set pressure arbitrarily, regular lump coal combined with gas chromatography analysis method was used to determine gas diffusion coefficient in lump coal, and gas diffusion law under different gas pressure and temperature was analyzed. The experimental results show that with increase of gas pressure, gas adsorbed by coal matrix increases and the coal matrix expand, thus pore decreases, diffusion resistance increases and diffusion coefficient decreases; with increase of temperature, movement speed of gas molecule increases, diffusion power enhances and diffusion coefficient increases.