Abstract: Taking coal sample in southern Qinshui basin for an example, we use the unsteady-state method to measure the relative permeability in gas and water displacement runs. Results indicate that gas displacement run show that the irreducible water saturation changed after each experiment, the relative permeability to gas was lower than to water. The coal samples tended to become more water-wet at high pressures in the case of adsorbing gases, namely methane and carbon dioxide, but in the case of non-adsorbing gas helium, higher pressure prevented the inflow of water into the pores leading to a decrease in irreducible water saturation with an increase in pressure. Water displacement run experiments were highly unstable based on the instability number calculated. The relative permeability curves showed oscillation. The experimental research suggests that the coal relative permeability to gas and water depended on the properties of gas, the pressure, and fluid-mineral interactions.