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Net ecosystem productive (NEP) is defined as the net carbon dioxide flux to or from an ecosystem without natural or human disturbance, and integrates all ecosystems carbon sources and sinks: NEE=GPP-Ra-Rh. Here NPP was calculated with the light use efficiency model based on NOAA/AVHRR, and the soil respiration of the corresponding ecosystem came from references. On the whole, the NEP shows the terrestrial ecosystem in China is a carbon sink though there are great uncertainties. The geographic gradient of the NEP clearly shows more correlation with temperature on latitude gradient, and with precipitation on longitude. Three main sources of uncertainties were analyzed: (1) land cover classification based on remote sensing; (2) NPP modelling; (3) soil respiration modelling. The observation and modelling integrated with remote sensing will be a very important solution to the carbon source/sink at large spatial sale.