Abstract: A state observer is designed for the case that the state of continuous linear plants can't be measured directly.Computing control signal based on plant model at intervals of signal transmission through network is addressed to reduce the usage of the network.Furthermore,necessary and sufficient conditions of global exponential stability are derived for a model-based NCS with delays.These conditions are affected by the network signal update time,the plant model error and network-induced delay.Simulation result illustrates the effectiveness of the stability conditions.