This paper is concerned with H_∞ output feedback control problem of networked control systems under denial-of-service attacks.Denial-of-service attacks are characterized by energy constraint jamming signal with periodic strategy,which attack wireless network channels and degrade system performance.Under the premise that the state of the system is partly unknown,by designing the observer-based output feedback controller,networked control systems under packet loss and denial-of-service attacks can maintain stable and pre-specified performance level.Finally,a numerical example is presented to verify the effectiveness of the designed controller.