Abstract: Taking shuangyong park in tianjin as a representative sample plot, the daily and seasonal changes of air ion concentration in the park and its different plant communities were measured to study the correlation between negative ions concentration and environmental factors. According to the unipolar coefficient and Abe air quality evaluation index the optimal time period of air quality in the park were selected to guide the surrounding residents to exercise outdoors in a suitable period of time. The results showed that from the observation results of negative ions concentration in the whole year, the negative ions concentration of evergreen conifer community showed spring>autumn>summer>winter; The performance of deciduous broad-leaved plant community was spring>summer>autumn>winter; The daily change of air ions concentration in urban parks showed a “U” shape change trend with the minimum value mostly between 13：30 and 15：30 and slight difference among different plant configurations. According to the assessment of the air quality CI of the park in spring, summer and fall, the optimal time period of the park’s air quality mainly distributed at 8：00-11：00 and 17：00, when the air reached the clean air standard and was more suitable for outdoor exercise for the surrounding residents; Whereas at 12：00 and 14：00 in the afternoon, the air was slightly pollutedI and it was not recommended to carry out outdoor activities for a long period of time.

Key words: city park, negative ions concentration, air quality, correlation of environmental factors