Traditional signal-free control roundabouts are suitable for intersections with lower traffic volumes. However, as traffic increases, they often become one of the main sources of urban traffic congestion. A large number of roundabouts in China face the issue of renovation. This achievement is based on Professor Yang Xiaoguang's first proposed and practiced 'Roundabout Left Turn Secondary Control Theory', which has formed optimization design techniques for roundabouts in terms of space and time, including spatial design for motor vehicle traffic and slow-moving traffic, as well as signal control technology, and layout design for non-standard roundabouts; it also includes methods for calculating major parameters in signal control such as phase sequence, green light duration, and phase loss time. The result provides a quantitative relationship between key influencing factors of the throughput capacity of signal-controlled roundabouts, allowing for the optimal determination of parameters such as the green light interval and the capacity of left turns on the ring road. And proposed the calculation method of straight and left-turn traffic capacity for signalized roundabouts. On this basis, it is possible to calculate and analyze the optimal combination of signal cycle, island radius and roundabout traffic capacity.