Abstract: In model-based networked control systems (MB-NC Ss) with multi-rate sampling, three different transmission policies including perfect transmissions, delayed transmissions and time-varying transmissions are in troduced. Necessary and sufficient conditions for global exponential stability are derived in the discrete time domain. Under the circumstance that the network bandwidth is determinate, a method for selecting the maximum communication interval which can guarantee the stability of discrete control system is presented an d the model error influence on the maximum communication interval with delayedt ransmissions is studied. It is also to be noted that the smaller the model error, the larger the maximum transmitting time.