In technological machines for various purposes, hydraulic actuators are widely used, which are constantly being improved in terms of the characteristics of power, speed and accuracy. These parameters must be stable, which requires making certain changes in the design of these actuators that allow them to withstand the operating modes of technological machines in the limits search. The authors consider results of the stability investigation of a nonlinear hydraulic actuator under the action of wave processes in its lines. They propose mathematical models of the wave process, which to some extent reflect its influence on the movement of the hydraulic motor in the form of a damping effect. For a nonlinear hydraulic actuator under the action of wave processes, a mathematical model and the results of the study of this hydraulic actuator are presented in the form of conditions, under which the stability of its operation is ensured.