The photodesorption model of Gortel, Kreuzer, and collaborators in which a laser is resonantly coupled to an internal vibration mode of an absorbed molecule is considered. The importance of including anharmonicity of the internal vibration and a broadening of energy levels of a zero‐order Hamiltonian is demonstrated. A numerical calculation of the photodesorption as a function of a laser intensity is presented for a multilevel system of CH3F on NaCl and compared with experimental data. In comparison to previous assumption of only harmonic motion for the internal vibration where the values of the laser fluences for laser‐stimulated desorption are calculated to be too low, our results (saturation intensities ∼105–106W/cm2) are in closer agreement with experiment.