Abstract: The urban public safety is seriously endangered by urban road collapse. The rapid, accurate and green detection of hidden dangers of urban road collapse will help reduce the development of urban underground diseases and improve the ability of urban safe operation. The main causes of urban road collapse in Chengdu City include complex geological structure, abundant groundwater and frequent humanistic engineering activities through investigation and analysis. The vehicle mounted three-dimensional geological radar is used to conduct a quick detection on urban roads, and a detection system is established based on detection, interpretation, verification, evaluation, results and information management. The results show that vehicle mounted 3D geological radar is an effective method for rapid detection of hidden dangers of urban road collapse.