In order to determine the generating capacity of negative air ions (NAIs) and its relationship with human activities, the NAIs in different functional areas of Hefei, China, were analyzed. And the half residence time was studied by simulated experiments. The results showed that the natural attenuation law of NAIs was complied with this equation: C(t) = 2986.6 × e–0.0141t. Based on the attenuation equation, the coagulation rate α = 0.0141, and the lifespan was about 49.16 min. Combined with the NAIs concentration monitored in different functional areas, it was found that there was a huge difference in background concentration and environmental production or consumption. The background concentration in urban forest area was much higher, indicating that plants were the main source of NAIs. Among them, the urban forest area (UF), water area (WA), culture and education area (CEA) and residential area (RA) produced NAIs, while others consumed. There was a threshold value for the consumption by human activities, which was generally no more than 30% and can reach 50% when the activity was intense. However, no threshold value was found for vehicle activities. These results can provide reference for other mid-latitude inland cities to optimize urban design, and build ‘resilient cities’.