Based on ground-penetrating radar (GPR) technology, this paper examined the formation characteristics, electrical properties, and morphological variations of common subsurface defects of urban roads. The paper summarized the radar spectrum characteristics of various subsurface defects, aiding in precise identification and providing a basis for subsequent assessment of road collapse risks. In addition, the paper integrated various factors, including subsurface defects, into the assessment of road collapse risk and established a “five-level” assessment model. This led to an integrated research approach for detecting subsurface defects and assessing collapse risks. A road project in Beijing was used as a case study, and a trapezoidal membership function was applied to assign values to collapse-related indicators. Fuzzy calculations were employed to determine the collapse risk levels for subsurface defects 1^#, 2^#, 3^#, and 4^#, classified as Level Ⅱ (low risk), Level Ⅲ (medium risk), Level Ⅲ (medium risk), and Level Ⅴ (high risk), respectively. The results indicate that low-risk defect 1^# requires enhanced routine inspections; medium-risk defects 2^# and 3^# necessitate regular inspections; high-risk defect 4^# demands immediate grouting reinforcement or excavation and backfilling.