Abstract: Optimal communication and control co-design of networked control system are studied in the paper.In p-to-w_σcommunication sequence where sensors access communication medium and m-to-w_ρ communication sequence where actuators access communication medium,the controlled object of the networked control system acts as a linear periodic time-varying system.Using lifting technology,the linear periodic time-varying system is converted to a linear periodic time-invariant system,and the linear quadratic performance index of the linear periodic time-varying system is converted to that of a linear periodic time-invariant system.The laws of optimal state feedback control and optimal output feedback control are given.