The need to take into account the dynamic processes that occur when performing technological operations using the working bodies of forest machines with a hydraulic drive is due to the fact that its absence leads to a distortion of the obtained results, since the kinematic schemes do not take into account the influence of hydraulic fluid in the elements of the hydraulic system. In this regard, it became necessary to develop models that take into account the dynamics of working body loading and the hydrodynamics of its drives. It is recommended to consider the influence of the process dynamics by introducing dynamic factors. The resulting mathematical model allows you to determine the actual values of the hydraulic cylinder, taking into account the errors associated with fluid leakage. As a result of the study, it was possible to connect the pressure change in the hydraulic cylinder, the movement of the pistons in the hydraulic cylinder and the rotor of the hydraulic motor, as well as the appearance of inertial forces. The connecting component is the balance of fluid and hydraulic system volumes.