With the rapid development of the urbanization, the problem of city transportation has been becoming the same issue to each big city in China. As the converge points of urban traffic, the branch junctions are playing important role in the road net and traffic flow. It is true that traditional PID control algorithm is widely used in various control systems. Because its principle is simple and easy to build and has no error in the steady state, etc. However, it does not have a good adaptability towards the change of parameters. It is inferior towards interference, etc. According to the above situation, a adaptive Fuzzy-PID control algorithm is proposed which has returned the characters of regular PID control algorithm. The fuzzy control algorithm is used to realize the on-line regulating relative PID parameters. The simulation analysis indicates that the presented method is effective to improve the main road control.