The application of systems with reference model self-adjustment and control signal saturation in a task of second-order dynamic object with uncertain or varied parameters is considered in this paper. The features of system behaviour at different values of the control object and model coefficients are analyzed. The condition of a self-adjustment process stability are formulated containing the system and model parameters only. The best quality criteria of a control processes are determined. The method of a system error and time constant reduction by the increase of self-adjustment signal amplitude is offered.