Abstract: In order to investigate the influences of gases that had different properties on the water- wettability of low rank coal,by used the low- field Nuclear Magnetic Resonance( NMR) Technology,the change of T2 spectrum during the process of water- saturation of wet coal powder under three kinds of condition,and wet coal powder re place with pressurized gases were analyzed. Results showed that in the process of water- saturation of wet coal powder,CO2 could reduce the ability of water imbibitions,b ut not the helium. In the process of the wet coal powder replace with pressurized gases,CO2 could transmit the adsorbed water to capillary water,the effect increased with CO2 gas pressure. In contrast,helium did not have this ability. A possible reason was that CO2 was easily to be adsorbed on coal inner pore surface,and change coal inner- surface property,resulting in a reduction of the interactions of coal- water and an increase of the contact angle of coal- water. It is concluded that CO2 gas has the ability to change the wettability of low rank coal,but helium has no effect on coal wettability.