Identifying and evaluating this effect is one of the key problems to be solved in urban forest management. In this paper, based on the measured data of 9 long-term monitored plant communities in Shanghai’s urban Park, a random forest model was established linking negative air ions and other indicators such as meteorological conditions and plant factors. Then, based on the long-term monitoring data of Shanghai Urban Forest Ecosystem Research Station and Shanghai Climate Center from February 2019 to January 2020 and the annual monitoring data of Shanghai forest resources, this paper evaluated the concentration of the negative ions of 105 typical forest resources in Shanghai, which covers Shanghai’s urban parks, ecological forestry, country parks, and green leisure spaces. The results showed that in 105 urban forest communities, the annual air negative ion levels were mainly Ⅱ and Ⅲ. The concentration of negative ions is higher in summer and autumn than in winter and spring. By drawing an oxygen bar map, it is found that the spatial distribution of urban forest oxygen bars in Shanghai is uneven. More forest oxygen bars should be built in the central area of Shanghai with high population density to meet the residents’ demand for health care. This study can provide a scientific basis for the rational use of forest oxygen bar resources in Shanghai to create recreational space for residents and provide a valuable reference for other urban forest management.