Abstract: 【Objective】 Evaluate the PM_2.5 retention capacity of a public park and discuss the effects of environmental factors on PM_2.5 concentrations in order to provide references for pollution control of PM_2.5. 【Method】 PM_2.5 concentrations within Beixiaohe Park in Beijing, indoor environment(the golf club)and along the roadside(open space)near the park were monitored to compare the differences in PM_2.5 concentrations in different environments. 【Result】 ① Diurnal variation in characteristics of PM_2.5 concentration in the three environments were the same. The results showed a curve with one “valley” between two “peaks”, indicating that PM_2.5 concentrations were high in the morning and at night and low during the daytime. ② When the air was not, or only slightly polluted, PM_2.5 concentration within the public park was lower than that indoors and along the roadside by 5.7% and 6.9%, respectively. This showed that the public park had a certain PM_2.5 retention capacity. When the air was mid-level polluted, PM_2.5 concentration within the public park decreased compared to that indoors and along the roadside by 3.6% and 7.3%, respectively, thus confirming the PM_2.5 retention capacity of the public park. When the air was highly polluted, PM_2.5 concentration within the public park was slightly lower than that along the roadside by 0.3%, and higher than that indoors by 5.5%. ③ PM_2.5 concentration within the public park was negatively correlated with air temperature and wind speed, and positively correlated with air humidity and air pressure. Moreover, PM_2.5 concentration along the roadside was positively correlated with vehicle flow rate. 【Conclusion】 When the air was not, or only slightly, or mid-level polluted, the public park had a certain PM_2.5 retention capacity, which was influenced by the local climatic conditions.