Abstract: According to the characteristics of the cyclic-service networks and the realtime requirements of three different kinds of data, periodic data, time-critical data and time-available data, the conditions of network stability are analyzed. A new bandwidth allocation scheme of dynamic sharing the time windows is proposed, which not only satisfies both requirements of real-timeliness and network stability, but also decreases the required buffer capacity and makes full use of the network resources. Furthermore, the effects of the bandwidth allocation of time-available data on the system performances are analyzed by simulation tests. It is shown that by proper choice of the bandwidth of time-available data both two kinds of bandwidth allocation of time-available data could guarantee the better performance of Networked Control Systems (NCSs).