Abstract: Excitation system of synchronous generator contained saturation element for effect of practical actuator,which had characteristic of saturation nonlinearity.This paper presented a novel approach based on regional method to design saturation excitation controller with input saturation element in excitation system.Firstly,extended state observer（ESO） was used to cancel internal uncertainty and external disturbance,and feedback linearization model of nonlinear system was gained.Secondly,an indicator of the degree of saturation of the ith entry of the control vector was applied to transform the saturation system into the polytopic system,and the conditions of the quadric stability of saturation system were expressed as matrix inequalities after dealing with the model of saturation system.Thirdly,the relation that the set of initial condition contained in the ellipsoidal region of attraction could be expressed as matrix inequalities in order to guarantee the local stability of saturation system.Thus,the problem of controller design considering of the set of initial conditions,region of attraction,and linear matrix inequalities（LMI） region,was transformed into solving the problem of bilinear matrix inequalities（BMI）.Finally,the validity of the proposed method and excellent control performance are illustrated in the case study.