Abstract: On the basis of analyzing the traffic flow operation of the freeway,the traffic characteristics of the freeway bottleneck were studied combining with the observed data.The results show that when the velocity of the flow is under 40 km/h or the occupancy is above 28%,congestion appears and the duration of the transition process from the stable flow to the forced flow is very short(less than 10 minutes).In addition, according to the analysis results of saturation flow rate of queue-before,queue-after and queue-developing,it is found that the service rate during the process of transfer from the stable flow to the forced flow is higher than that of the stable flow or the forced flow,so that the capacity of the freeway section obtained from flowvelocity curve model is overestimated.