Abstract: Traffic congestion is one of the common urban traffic problems in people's travel. lt is impor-tant to monitoring the traffic congestion situation , analyzing the causes of traffic congestion , and then im-proving the traffic congestion . Taking the main urban area of Kunming city as an example , based on thereal-time road condition data provided by Amap, this paper designs a congestion time-space index to eval-uate the traffic condition in the study area and analyze its spatial and temporal characteristics, and ana-lyze the causes of congestion from the perspective of road network structure. The results show that: 1)The congestion time-space index can effectively evaluate the spatial and temporal characteristics of trafficcongestion in a long time series, and the applicability of the evaluation index is strong. 2) The overalltraffic situation in the study area is good. The average proportion of free passage sections is 72% , and the average proportion of congested sections is 5% , and the overall traffic situation changes more regularly3) The traffic congestion in the study area has significant temporal and spatial aggregation characteristics.There are few road sections that are congested for a long time, and the slow-moving areas are mainly onurban main roads; morning peaks and evening peaks of the day appear between 8: 00-8: 30 and 18 ;00-19: 00; weekends are compared with weekdays. Congested road sections and congestion time aresignificantly reduced, the congestion time-space index change curve is relatively stable, and changes intraffic situation are significantly affected by commuting. 4) Among the impact factors of the road networkstructure , the density coefficient of traffic nodes is the largest and is positively correlated with the conges-tion time-space index. A reasonable control of the number of traffic nodes is an important way to alleviatetraffic congestion in the main urban area of Kunming city.

Key words: urban traffic situation, traffic congestion evaluation, traffic congestion time-space index, rea-sons for traffic congestion, Kunming