This paper proposes an active control system for urban road traffic,with the purpose to provide a new way to realize the intelligent control of urban traffic and alleviate traffic congestion.The system is composed of four subsystems.The cloud-side-end support subsystem constitutes the basis of computing,communication and storage.The visualized hardware- and software-in-the-loop subsystem is the key to command,make decision,and exercise in traffic control.The real-time control subsystem and real-time simulation subsystem constitute the core of traffic control operation,which can guarantee the real-time and advanced traffic control.Instead of traditional passive control of intersection signals relying on cycle and green ratio adjustment,the system adopts an active control of intersections characterized with variable lanes,adjustable phase sequence and chain connection features.Experimental analysis shows that the system can effectively reduce the total delay time and average queue value of vehicles waiting on the traffic lights at the intersection.