Abstract: 【Objective】 It is important to study quantitative evaluation of CO2 fixation and O2 release function in ecological system. This article attempts to measure and evaluate the value of fixing carbon and releasing oxygen in land ecological system using remote sensing, to provide reference for the regional ecological environment. 【Method】 Based on photosynthesis, using remote sensing estimation model, based on the results from the electroosimosis NPP vegetation, the fixed carbon and released oxygen amount was estimated. Based on this result, by using forestation costs method and the industrial oxygen producing method, the values of fixed carbon and released oxygen in Loess Plateau in Northern Shaanxi Province were estimated. The spatial and temporal changes and distribution of the fixed CO2 and released O2 in loess plateau ecological system were discussed. 【Result】CO2 fixation values in Loess Plateau in Northern Shaanxi Province in 1978, 1990, 2000 and 2005, respectively, were141.27 billion yuan, 177.46 billion yuan, 170.09 billion yuan and 247.08 billion yuan, and the average was 187.72 billion yuan. The value of O2 release from the two evaluation methods, averaged, respectively, 150.07 billion yuan, 188.52 billion yuan, 192.97 billion yuan and 281.48 billion yuan, and the annual average was 203.26 billion yuan, more than an average of CO2 fixation 15.54 billion yuan. From the perspective of land use types, forestland＞cultivated land＞grassland＞garden＞other types. 【Conclusion】 The value of the fixed CO2 and released O2 in loess plateau ecological system of northern counties is lower than southern counties and in general distribution along the northern south to increasing gradually. HuangLong Mountain in south has the very high ridge and unit area of value, such as the county, Huangling county, Fu county and Ganquan county. The value of fixing carbon and releasing oxygen in northern agriculture and animal region and the central loess endangers region with the serious soil and water loss has lower value, this fragile ecological environment and relevant.

Key words: NPP, land ecosystem, fixing carbon and releasing oxygen, Loess Plateau in Northern Shaanxi Province