Abstract: In view of the gaps existing in the adsorptive characteristics research of extra high rank coal whose vitrinite has the maximum reflectance(R_o(max))of more than 4.0%,twelve coal samples(R_o(max)>4.0%)were collected systematically and conducted a high pressure and isothermal adsorption experiment under the condition of equilibrium moisture content,and the relationships between the Longmuir constant of extra high rank coal samples and R_o(max),maceral,specific pore volume or specific surface area were analyzed.It was found that inflection point on the curve of Longmuir volume vs.coal rank is around R_o(max)=4.5%.On the basis of above research,the adsorptive characteristics and mechanism of coal were discussed.