Abstract: Aim of this paper is to study the validation of gross primary product (GPP) from MODIS in monitoring winter wheat ecosystem of Huabei Plain, which is characteristic of heterogeneity , and the carbon source/ sink function of this crop ecosystem. Firstly, based on the phenological curve of winter wheat, a decision tree was designed to extract the winter wheat area from the MODIS-NDVI product. The classification map was also cross-validated by the high resolution classification map from the multi-temporal Landsat TM images, with an user’s precision of 90.6% and an overall precision of 87.2%. Then, combined with MODIS-GPP product, the whole growth seasonal GPP of winter wheat of Huabei Plain in 2010 was calculated. The MODIS-GPP product was validated by the observed eddy covariance data, with a determination coefficient of 0.9227; The winter wheat’s GPP in Huabei Plain is 6.24′108 kgC , which is about 21.3% of the total GPP in Huabei Plain; Finally, according to the respiration of ecosystem (RE) and net ecosystem productivity (NEP) calculated from eddy covariance flux measurements, the winter wheat in Huabei Plain holds high capability to fix carbon, the ratio of NEP to GPP is 58.7%.