Negative air ions (NAI) have garnered significant attention from governments at all levels and the public in recent years due to their diverse biological effects and environmental health benefits, which are closely linked to ecological environment quality and forest therapy services. NAI concentration effectively reflects atmospheric and human habitat quality, serving as a key indicator for assessing ecological environment quality and forest therapy potential. Existing research indicates that NAI typically exhibits significant diurnal periodic fluctuations and seasonal variations across temporal scales, though specific patterns differ markedly across regions and ecosystems. Spatially, NAI concentrations generally follow a distribution pattern where natural ecosystems exceed urban built environments, vegetated areas surpass bare and hard surfaces, water-rich environments outperform water-deprived ones, and outdoor environments demonstrate higher concentrations than indoor environments. Regarding influencing factors, environmental variables such as temperature, humidity, wind speed, solar radiation, and air quality collectively affect NAI generation and maintenance by regulating air ionization processes, ion stability, pollutant loads, and vegetation physiological activities. Concurrently, biological factors including plant species, forest types, and stand structures exert significant long-term regulatory effects on NAI concentrations by altering microclimate conditions, photosynthetic oxygen supply capacity, and air cleanliness. This paper systematically summarizes the spatio-temporal variation characteristics of NAI and its primary environmental and biological influencing factors. It identifies existing gaps in current research regarding monitoring techniques, analysis of influencing factors, quantification of health effects, and development of predictive models. Consequently, future research directions are proposed to deepen the understanding of NAI's spatio-temporal patterns and influencing factors, thereby providing theoretical support for ecological environment quality assessment and the scientific utilization of forest therapy resources.