Abstract: In order to investigate the swelling deformation effect of coal induced by pore pressure and gas adsorption, the solid-flow coupling experimental equipment was used to perform the axial and lateral deformation test of coal under different gases (Ar, CO₂, CH₄) and different pore pressures under the constant temperature and pressure conditions. The results show as follows: the coal deformation caused by pore pressure increases with the increase of pore pressure. The coal deformation caused by adsorption increases with the increase of pore pressure. And the axial strain is greater than the lateral strain. The effective stress coefficient α influenced by pore pressure and adsorption, it can be expressed as α=α₁+α₂. Both the effective stress coefficients α₁ and α₂ follow the bilinear law with respect to pore pressure p and volume stress Θ. The effective stress coefficient α is anisotropic, and the effective stress coefficient perpendicular to the bedding direction is greater than the effective stress coefficient parallel to the bedding direction.