Four coal samples of different ranks are selected to perform the adsorption measurement of high-pressure methane (CH4). The highest equilibrium pressure of the measurement exceeds 20 MPa. Combined with the measuring results and theoretical analyses, the reasons for the peak or the maximum adsorption capacity appearing in the excess adsorption isotherms are explained. The rules of the peak occurrence are summarized. And then, based on the features of coal pore structure, the adsorption features of high-pressure gas, the microcosmic interaction relationship of coal surface and CH4 molecule, and the coalbed methane reservoir conditions, three theoretical assumptions on the coal adsorption high-pressure CH4 are suggested. Thereafter, on the basis of these theoretical assumptions, the Ono-Kondo lattice model is processed for simplification and deformation. Subsequently, the equations modeling the excess adsorption isotherm of high-pressure CH4 adsorption on coal are obtained. Through the verification on the measurement data, the fitting results indicate that it is feasible to use the Ono-Kondo lattice mode to model the excess adsorption isotherm of high-pressure CH4 adsorption on coal.