<p>Nitrogen is indispensable for global food production and ecosystem carbon sequestration, but excess nitrogen leads to water eutrophication, soil acidification and air pollution. Atmospheric nitrogen deposition is a key yet uncertain component of the biogeochemical cycle. Currently, global networks monitoring particulate nitrogen dry deposition rely mainly on measured concentrations and modelled dry deposition velocities, which remain poorly constrained. Here we develop a spatially explicit dataset by integrating observation-constrained size distribution and dry deposition mechanisms to re-evaluate atmospheric nitrogen deposition across China. We reveal that atmospheric chemistry models underestimate the particle size of fine-mode nitrogen-containing aerosols in China by more than twofold. Additionally, dry particle deposition velocity estimates with different mechanisms diverge by up to two orders of magnitude. Our corrections indicate that atmospheric chemistry models and China’s observation network underestimate particulate nitrogen dry deposition by 2–5 times. Furthermore, most Earth system models underestimate particulate dry deposition of ammonium, a major nitrogen species, by 31%–98%. By integrating these corrections into the Community Land Model, we demonstrate that the effect of nitrogen deposition on China’s terrestrial net ecosystem productivity may have been underestimated by 9%–13%. As China contributes nearly 20% of global nitrogen deposition, its impact on terrestrial carbon sinks and ecosystem health could be greater than previously recognized.</p>