A simulation computer model was developed with a view to conducting the simulation of modes of dynamic loading of mechanical oscillatory systems of the single-stage evolvent helical tooth gears class. The model implementation was carried out by means of the MatLAB-Simulink simulation environment, based on the principles of analog simulation. Schematics of the computer simulation model and the generator of external loading functions were presented. Internal structure of the block for solving one of the equations of mathematical model in mechanical oscillatory systems was established. In the course of modeling experiment, we performed simulation of the modes of dynamic tooth gear loading by force, the loading moment of which is simulated by the function of stepwise or linear-increasing character. Results of the simulation results were obtained in the form of combined oscillograms of the alternating moment of external loading and reactions in the form of oscillations of one of the elements of the tooth gear structure. The simulation was carried out with the assigned values of weight and rigidity, damping, geometric, structural and dynamic parameters of mechanical oscillatory systems. Obtained experimental results allow assessing the values of dynamic forces in tooth gear nodes depending on the ratio of rotation periods of the shaft, and function of changing the external loading moment, subject to the action of stepwise and linear-alternating forms of the force.