The ??∞ filtering for networked control systems with stochastic transmission delay longer than a sampling period and data packet dropout is studied. For the given packet dropout, the filtering error system is modeled as an asynchronous dynamical system with rate constraints on two events. The sufficient condition for guaranteeing the exponential stability and the ??∞ constraint of the filtering error system is given by using the theory of asynchronous dynamical systems. The corresponding filter is designed by solving a set of matrix inequalities. The simulation result shows the validity and effectiveness of this method.