Аннотация:The rigorous technique of numerical simulation of two-frequency laser excitation of vibration-rotational levels of molecules in the collisional conditions is offered for the first time. The density matrix equation of three-level system accounting for the processes of laser pumping, impact line broadening and RT relaxation is used to derive the analytical expressions for probabilities (rates) of single- and two-photon laser excitations. With using of these results rate equations for populations of three vibrational levels are obtained allowing simulating correctly the processes of single- and two-photon vibrational excitation in the collisional conditions accounting for the rotational structure of vibrational levels. The algorithm of data reduction of real molecular spectra of arbitrary complexity to the set of equivalent three-level vibration-rotational systems which can be carried out with using the HITRAN database is described in detail. The operability of the offered theoretical technique is illustrated by the example of the laser excitation of low vibrational levels of О3 molecules. An exact analytical temporal behavior of level's population is developed. The contribution of processes of cascade and two-photon excitation is analyzed. The comparison with experimental data is made