The amount of oxygen in the atmosphere directly affects air quality. Photosynthesis of terrestrial green vegetation is the main source of oxygen for the atmosphere. Therefore, simulating oxygen production generated from terrestrial vegetation has been used as a popular approach to assessing atmospheric environment quality. With the C-FIX model in this study, we simulated the Net Ecosystem Productivity (NEP) from the Normalized Difference Vegetation Index (NDVI) and climatic data such as temperature and radiation. Following the principle of the carbon-oxygen balance, annual oxygen productions of terrestrial vegetation in China in 2001, 2005, and 2009 were spatially estimated in ArcGIS, and their influencing factors were analyzed via model simulation. Our results suggest that (1) the total annual oxygen production of terrestrial vegetation in China is 531.618×10⁷ t. The provinces of Yunnan, Heilongjiang, and Sichuan and the Inner Mongolia Autonomous Region contribute the largest source of oxygen, accounting for more than 35×10⁷ t. Provinces of Hunan, Jiangxi, Hubei and Autonomous Regions of Guangxi and Tibet have the total oxygen production higher than 20×10⁷ t. Areas with the lowest amount of oxygen production include the provinces of Taiwan, Hainan, the municipalities of Beijing, Tianjin, Shanghai, Hong Kang Special Administrative Region, and Ningxia Autonomous Region, accounting for 5×10⁷ t in total. (2) A significant seasonal change in terrestrial oxygen production is detected with the highest totals occurring in the summer (259.438×10⁷ t), about twice of the total in spring and fall, and eight times higher than that in the winter. Yunnan and Sichuan provinces have the highest production in the spring. The Inner Mongolia Autonomous Region and Heilongjiang Province have the highest in the summer, while Yunnan and Guangxi Autonomous Region have the highest in fall and winter. (3) Oxygen production in China shows a basic descending trend from southeast to northwest. The highest totals are located in Fujian, Zhejiang, Taiwan, southern Yunnan, and southeastern Tibet. Seasonally, there is a spatially significant variation in peak oxygen production, with the highest occurring in southern Yunnan, southeastern Tibet and east China in the spring, Daxinganling and Xiaoxinganling Mountain ranges in the summer, along the southeastern coast, Yunnan, and southeastern Tibet in the fall, and over southern Yunnan and Hainan Provinces in the winter. (4) Overall there is an increasing trend of oxygen production by terrestrial vegetation across China between 2001 and 2009 with a growth rate of 8%. The highest growth rates are observed in Ningxia Autonomous Region (>48%) Shanxi Province (35%), and provinces of Shaanxi, Hainan and Yunnan (20%) In contrast with the generally increasing trend in most areas, provinces of Xinjiang, Inner Mongolia, Guizhou, Chongqing, Shanghai, Hubei and Hunan reveal decreasing trends, in which Hunan reaches the highest decreasing rate of 10%. (5) Our results also indicate that the changing vegetation cover is the most significant factor in influencing the elevated oxygen production, accounting for 60% of total change. The increases in CO₂ and climate change contribute about 28% and 12%, respectively. Regionally, the increased vegetation cover plays a major role in northern China, while climate change is the major control in southern China.