To effectively prevent and control urban high slopes and reduce safety risks, two third-level high slopes at the east start (about 60 m) and end (about 40 m) of a secondary arterial roads in a city in Hunan are taken as research subjects. Considering excavation costs and slope safety and stability requirements, a combination of qualitative and quantitative analysis methods is adopted to determine the optimal excavation slope ratio scheme and propose post-excavation protective measures. The results show that when using slope ratios of 1.00:1.25, 1.00:1.00, and 1.00:1.00 from top to bottom, the stability coefficients under natural and rainstorm conditions are 1.25 and 1.01, respectively, which do not meet code requirements; when the combination of slope ratios of 1.00:1.50, 1.00:1.25, and 1.00:1.25 are used, the stability coefficients for both conditions are 1.436 and 1.158, respectively, thus meeting code requirements. Further qualitative analysis shows that the stability coefficients under this slope ratio combination can reach 2.209 and 1.805, both meeting safety requirements. In view of the high and steep rear wall of the slope, the well-developed joints and fissures, and the fragmented rock, wedge-shaped slippages and translational failures along the bedding planes are likely to occur. Therefore, it is proposed to adopt the combination of "slope surface leveling + bolted frame" for the first-level slopes, and "slope surface leveling + diamond-shaped framework with grass planting" for the second-level and third-level slopes as protective measures. The results can provide a basis for the design and construction of urban road slope support.