In this poster we introduce a new 3-year project (1/1/2005 – 12/31/2007) under the support of NASA, as part of NASA Carbon Cycle Science and Northern Eurasia Earth System Science Partner Initiative (NEESPI) programs. A limited number of CO2 eddy flux tower sites, distributed over vast terrain of Northern Eurasia, provide valuable continuous observations of net ecosystem exchange (NEE) between forests and the atmosphere. It is a grand challenge to scale-up the in-situ flux data across landscape and region. We proposed to combine an innovative satellite based Vegetation Photosynthesis Model (VPM) and a process-based biogeochemical model (DNDC) for conducting diagnostic analysis of spatial and temporal variation of CO2 flux from forests in Northern Eurasia. Our major objectives include (1) improving quantification of CO2 fluxes of forests in Northern Eurasia and (2) developing and evaluating a data-model assimilation system for biogeochemical analysis at large scales.