Abstract: Based on the survey data of 45 sample plots in Luoping County, Yunnan Province, the relationship between tree species diversity and ecosystem multi-functionality in urban green space was investigated by using the mean method. Four ecosystem function variables were selected, including green quantity, cooling, humidfication and noise reduction. The results show that the comprehensive index K of tree species diversity in different green spaces in Luoping County is ranked from high to low as park green space(1.76) > street green space(1.68) > residential area green space(1.64) > enterprise green space(1.59) > campus green space(1.33). The tree species richness index(G) is significantly positively correlated with green quantity, humidification, and cooling, and has no significant impact on noise reduction; Simpson index(D) and Shannon−Wiener index(H) has a significant positive correlation with green quantity, cooling, humidification and noise reduction; uniformity index(J) has a significant positive correlation with green quantity, noise reduction and humidification, but no significant correlation with cooling. There is a very significant positive correlation between the diversity of urban green space tree species and ecosystem multi-functionality, and the Shannon−Wiener index has the greatest impact on multi-functionality(R²=0.694, P<0.01), indicated that maintaining multiple ecological functions at the same time required more abundant plant and species. The diversity of urban green space tree species is of great significance to the function of ecosystem. Compared with a single function, it has a greater influence on multi-functionality.