The article deals with the problem of synthesis of control, providing temperature maintenance in the jacket of the CSTR reactor. The standard mathematical model, describing the reactor operation, has been extended by introducing the following dynamics of the executive device and consideration of physical restrictions of the state and control vector components. Under conditions of incomplete information about the state vector and at influence of external disturbances, an observer of the state and disturbances is synthesized, allowing to receive estimations of unknown signals with the set accuracy. The use of the block approach allowed to take into account physical constraints on phase variables and control at the stage of feedback synthesis. The proposed approach showed high efficiency by modeling the system CSTR reactor - DC motor in the Matlab simulation experiment.