Abstract: An intelligent PID controller is designed to adjust ABR traffic rate on-line in ATM network for the congestion of high-speed communication networks with a Smith predictor introduced in to avoid the adverse effect of roundtrip propagation delay on control. The improved PSO algorithm is introduced in tuning the parameters of PID controller. The controller designed is independent of the mathematic model of networks, thus getting rid of the adverse effects of such uncertainties as the number of users, ABR bandwidth and propagation delays on network performance and ensuring the fair distribution of bandwidth and full utilization of links. Simulation results show that the control system is stable and robust with QoS guaranteed.