Roundabout is a widely used traffic control system throughout the world and usually established in the road network of large cities. It can improve traffic flow and safety. In Macau, some roundabouts are used at intersections to control traffic flow. Since Macau is the most densely populated city in the world, roundabouts with short and narrow approaches are common in Macau. The efficacy and characteristics of roundabout in urban road network are the main interests to study. In order to understand the performance of urban road network with roundabout, the geometry of and traffic flow at two essential roundabouts in Taipa were measured. From those measurements, a simulation model developed by simulation tool. To evaluate the effect of different scenarios at the roundabout, three scenarios are simulated based on the original model: (1) removing the current bus stop from one of the roundabout, (2) removing the zebra crossings from roundabouts, (3) lengthening the distance between two roundabouts. Through these three scenarios, the causes of urban roundabout’s traffic congestion can be know, and improve understanding of performance and analyzes the simulation result of these two roundabouts, including the delay and level of service. The findings from these three scenarios are as follows. The bus stop in the roundabout had no major effect on the performance of roundabout because the bus stop has a low usage rate. The zebra crossings in the approaches of roundabout are contrary to the safety and performance of roundabout. The distance between two roundabouts had no significant effect on the performance of roundabout. Furthermore, traffic signals can be installed at roundabout to control the traffic flow, Installing traffic signals at the two simulated roundabouts showed that traffic signals can effectively improve traffic congestion; because they can control transit time according to the traffic volume in each entry lane. If no measures are taken to improve traffic, the traffic condition in Macau will face challenges. This study verified that signal control seems to be a good choice to improve the traffic congestion.