The correlation between negative air ions (NAI) and nitrogen oxides (NOx) exhibits significant seasonal characteristics and is non-static. Previous studies have shown that NAI concentration is highly sensitive to meteorological factors, while NOx concentration is also affected by meteorological factors, resulting in potential differences in their correlation under different meteorological conditions. To deepen the understanding of this relationship, this study explored the impact of different meteorological factors on the correlation between NAI and NOx. The main conclusions are as follows: (1) The interaction between NAI and NOx in urban forests is regulated by meteorological factors; the higher the temperature, humidity, and solar radiation, the larger the correlation coefficient, and the stronger the negative correlation between the two; (2) Under synergistic meteorological conditions, NAI concentration is high and NOx concentration is moderate, which is suitable for outdoor activities: Condition 1 is temperature > 20 °C, humidity 30–60%, air pressure > 940 kPa, solar radiation 30–60 W·m⁻², wind speed < 1 m·s⁻¹; Condition 2 is temperature > 20 °C, humidity > 60%, air pressure > 940 kPa, solar radiation > 60 W·m⁻², wind speed < 1 m·s⁻¹ (based on NAI and NOx concentration data and health standards: NAI ≥ 1000 cm⁻³ is beneficial to health, and NOx ≤ 80 μg/m³ meets WHO limits); (3) Temperature, humidity, and air pressure have regulatory effects on the relationship between NAI and NOx, among which air pressure exerts positive regulation, while temperature and humidity exert negative regulation.