The distribution characteristics and factors influencing the underground roots of urban street trees were studied to provide a scientific basis and data support for the healthy growth and maintenance management of these trees. Eight main tree species along the roads of Longzihu University Park in Zhengzhou were selected as the research subjects. The distribution characteristics of the root systems of the street trees were analyzed and summarized using a tree radar detection system. Additionally, three physical soil indexes, water content, compactness, and soil temperature, were measured to explore the physical soil factors affecting root distribution. The results indicate that: (1) In the horizontal direction, the root density of street trees is evenly distributed across the three scanning radii; in the vertical direction, the root density is primarily concentrated at depths of 20～40 cm. (2) There are significant differences in root distribution among various tree species. (3) The density of thick roots shows a significant positive correlation with soil water content and a significant negative correlation with soil compactness. In urban road environments, the root distribution of street trees is shallow, which is influenced not only by the unique urban environment but also by soil water content and compactness.