Lung cancer remains the primary cause of death globally. Studies have increasingly explored the role of greenspace in mitigating lung cancer risks, yet research gaps persist. First, while the direct spatial effect of greenspace has received attention, its potential spillover effects, driven by human mobility and air pollution dispersion, remain underexamined. Second, despite prevalent assertions of greenspace as an air purifier, the extent to which it moderates the air pollution-lung cancer association has yet to be fully understood. Third, the evaluation of greenspace's effects, predominately analyzed linearly a priori, demands exploration into their potential nonlinearity. We utilize three-year lung cancer datasets from 228 counties in China, to investigate the spatial, moderating, and threshold effects of greenspaces on lung cancer incidence in relation to air pollution. Employing spatial econometric and threshold models, our findings indicate that greenspace reduces lung cancer incidence in both local and neighboring counties. We also observe a diminution in the detrimental impact of air pollution on lung cancer incidence in areas with higher greenspace, especially when the Normalized Difference Vegetation Index surpasses a given threshold. These insights contribute to an enhanced understanding of greenspace's role in lung cancer prevention and could inform policies on greenspace expansion prioritization.