Three-dimensional green biomass can indicate the benefits of urban ecosystems. Sixty representative plant communities (20 m × 20 m) in seven parks were selected as sample plots in Nanping City, China. The structural characteristics, three-dimensional green biomass per square meter (PGB), and ecological benefit value of the plant communities in each plot were measured. The results showed that the PGB of Jiufengshan Park was the highest, reaching 5.60 m³·m-2. The Random forest model revealed that the coverage, diameter at breast height (DBH), and tree number had a highly significant effect on PGB (P < 0.01), and tree crown width had a significant effect on the PGB (P < 0.05). Therefore, the PGB of parks can be improved by improving the coverage, DBH, tree number, and tree crown width, which would help to increase the ecological benefit value and well - being of human beings.