<p>Hypertension (HTN), a major contributor to cardiovascular diseases, is linked to ambient air pollution and residential greenness. However, their joint associations remain unclear. This research focuses on assessing the individual and joint associations of ambient air pollution and residential greenness on HTN among Northwestern Chinese adults. In this cross-sectional analysis, 4,214,199 participants in Northwestern China were included. HTN was assessed via standardized assessment protocols. Air pollutant concentrations were estimated via the Space-Time Extra-Trees model, and greenness was assessed through the Normalized Difference Vegetation Index (NDVI). Generalized regression models were employed to assess the individual and joint effects of air pollutants and residential greenness on HTN. The prevalence of HTN was 20.43%. The adjusted odd ratio of HTN for each 10 µg/m³ increase in PM1, PM2.5, PM10 and SO2 were 1.571 (95% CI: 1.556–1.585), 1.070 (95% CI: 1.068–1.072), 1.021 (95% CI: 1.020–1.021) and 1.798 (95% CI: 1.770–1.827), each 0.1-unit increase in NDVI were 0.943 (95% CI: 0.940–0.946) respectively. The negative association of residential greenness with HTN appeared to weaken at higher concentrations of air pollutants. Mediation analysis indicated that body mass index (BMI) partially mediated the effects of both air pollutants and NDVI on HTN risk. Our findings reveal that air pollutants are positively correlated with HTN, while residential greenness shows a negative association. However, this negative association is attenuated at higher concentrations of air pollutants. Additionally, the associations of air pollutants and residential greenness with HTN appear partially mediated by BMI</p><p></p>