Understanding the spatial distribution pattern of spontaneous plants in cities is helpful for planning and managing the urban plant landscape. To explore the distribution pattern of urban spontaneous plant diversity, we used the 5th Ring Road of Beijing as the study area in this research. A total of 252 sample sites were selected and surveyed from September to October 2020. Combined with indicator Kriging methods, the geographical detector model (GeoD), and Pearson correlation analysis, we analyzed the spatial distribution pattern and the mechanism that influenced the spontaneous plants in Beijing urban area. As the results, a total of 173 plant species were recorded, which belonged to 144 woody plants and 29 herbs. There were significant differences in the spatial distribution pattern of herbaceous and woody spontaneous plants. Herbaceous spontaneous plants had a significant urban-rural gradient, which showed that the diversity of herbaceous plants increased from the urban center to the urban suburbs. Woody spontaneous plants showed local high-density areas rather than urban-rural gradients. The distance from the city center, socio-economic variables, and the intensity of green space management were the dominant factors that affected the spatial distribution pattern of herbaceous spontaneous plants. The spatial distribution pattern of woody spontaneous plants was affected by the interaction of green space management intensity, house price, and the distance from the city center. The results help in deciding priority areas for the future to protect biodiversity and offer insights into urban green space planning and management.