Trees situated in urban environments with substantial pedestrian activity are exposed to elevated safety hazards owing to the dense concentration of both pedestrian and vehicular traffic. Furthermore, conventional tree risk assessment methodologies often encounter challenges in identifying potential hazards in a comprehensive and objective manner. This study innovatively integrates traditional Visual Tree Assessment (VTA) and Non-Destructive Testing (NDT) techniques, employing the Bund and Nanjing East Road as research locations. Based on visual assessment, PICUS-3 acoustic tomography and TRU radar techniques are utilized to detect the trunk cavitation and root conditions, thereby facilitating the development of a comprehensive tree risk assessment system. The results indicated that the majority of the trees exhibited minimal or no trunk hollow rot. Moreover, the extent of hollow rot generally demonstrated a pattern of progressive worsening from the apex to the base of the trees, suggesting a phenomenon of mutual infection of trunk hollow rot. As for the root system, most of the trees had a relatively uniform distribution density of coarse roots, but some trees had missing roots. In addition, trunk hollow rot and root density did not show a significant correlation. More than 80% of the trees in the two high-traffic areas had risk ratings in the acceptable or negligible range. Yet approximately one-third of the trees exhibited a significant risk to their root systems, posing a safety hazard. Three risk factors had the highest frequency of root deficiency, with trunk hollow rot and stem-boring pests being the next most frequent problems. The study provides new ideas and technical support for urban tree safety management, which is important for improving tree safety in high-traffic areas.