A new approach to robust control systems synthesis, both linear and nonlinear, and non-stationary is offered. The control is carried out, providing the given phase constrains varied in acceptable limits, in view of constraints on its value and incompleteness of the information about functioning disturbances. The approach is based on introduction of auxiliary integral surfaces, on which the initial moving is projected. As a result the reduced equivalent moving is formed, being described by the scalar equation which in many important cases can be integrated directly. On the basis of the equation obtained solving a synthesis task is carried out and can be reduced to algebraic or integral inequalities. The final relations defined for linear equivalent moving are presented.