Abstract: Considering the influence of networked quality-of-service (QoS) on the control performance, a system model combining the network parameters and the control parameters is established for networked control systems (NCSs). Based on this, the condition dependent on the network parameters and control parameters is presented for the existence of guaranteed cost controllers. Furthermore, the parametric design method of the controllers is given by solving the linear matrix inequality (LMI). Within the scope of QoS perturbation, the designed controller can not only make the system asymptotically stable but also guarantee that the system performance index is not greater than the upper bound. The proposed method gives the quantitative relation between the QoS change and the attenuation of control performance, which provides the theoretical accordance for the scheduling of NCS.