Abstract: In order to explore the influence of water and salinity on the methane adsorption capacity of coal samples, the isothermal adsorption experiments of coal samples with water saturation and water with different salinity were car-ried out using the coal samples from the middle Jurassic Xishanyao formation block in the Manas mining area of the southern margin of Junggar basin. The results show that the Langmuir volume of dry coal sample was significantly lar-ger than that of distilled water injection sample,and the Langmuir volume of distilled water injection sample was larger than that of water injection coal sample with salinity being 10 000 mg / L,but the latter is close to that of water injec-tion coal sample with salinity degree of 20 000 mg / L. The main reason is that the distilled water molecules can be more easily adsorbed on the surface of the coal matrix than methane molecules,which makes the reduction of Langmuir volume. The salinity water further reduces the adsorption sites of coal matrix surface,resulting in the reduction of meth-ane adsorption capacity of coal samples. However,there is a limit salinity value,and the water with salinity degree greater than 20 000 mg / L cannot significantly reduce the Langmuir volume of coal samples. Therefore,it can be in-ferred that in the groundwater runoff area or weak runoff area,when the salinity degree of coal seam water increases continuously to 10 000 mg / L,the content of free gas in the coal seam will increase,while the content of adsorbed gas will decrease. When the salinity degree of coal seam water exceeds 10 000 mg / L,both the content ratios of adsorbed gas and free gas in coal seam tend to be stable.