This paper investigates urban traffic data by analysing the long-range correlation with detrended fluctuation analysis.Through a large number of real data collected by the travel time detection system in Beijing,the variation of flow in different time periods and intersections is studied.According to the long-range correlation in different time scales, it mainly discusses the effect of intersection location in road net,people activity customs and special traffic controls on urban traffic flow.As demonstrated by the obtained results,the urban traffic flow represents three-phase characters similar to highway traffic.Moreover,compared by the two groups of data obtained before and after the special traffic restrictions(vehicles with special numbered plates only run in a special workday) enforcement,it indicates that the rules not only reduce the flow but also avoid irregular fluctuation. This paper investigates urban traffic data by analyzing the long-range correlation with detrended fluctuation analysis. Through a large number of real data collected by the travel time detection system in Beijing, the variation of flow in different time periods and intersections is studied. According to to the long-range correlation in different time scales, it mainly discusses the effect of intersection location in road net, people activity customs and special traffic controls on urban traffic flow. As demonstrated by the obtained results, the urban traffic flow represents three-phase characters similar to highway traffic. More than, the two groups of data obtained before and after the special traffic restrictions (vehicles with special numbered plates only run in a special workday) enforcement, it indicates that the not only reduce the flow but also avoid irregular fluctuation.