The structural principle of highorder rectilinear flexible system was analyzed and the mathematical model of 3-DOF rectilinear flexible system was established.In rectilinear flexible system,the position information of mass block could be obtained,but the speed state information was not readily available.Aiming at the character,the controller was designed based on detectable system states.It was difficult to be quickly stabilized for flexible structure system existing disturbances.Therefore,robust guaranteed cost control based on observer was designed.Experimental results demonstrate the effectiveness of the control scheme.