Abstract: By using the EOS/MODIS NPP data of remote sensing biogeochemical model (BIOME-BGC), this paper analyzed the spatiotemporal variations of vegetations carbon fixation quantity in the reforested croplands of Shaanxi Province, China in 2000-2010, and estimated the service values of the vegetation carbon fixation and oxygen release, according to the specifications for the assessment of forest ecosystem services in China. From 2000 to 2010, the estimated carbon fixation density in the reforested croplands was averagely 299 g·m^-2·a^-1. As compared to the year 2000, the amount of carbon fixation in the reforested croplands in 2010 increased by 5.37×10⁶ t·a^-1, and the carbon fixation value totaled 1.401 billions Yuan, accounting for 50.4% of the increment value of the carbon fixation in the Province, while the area of the reforested croplands only occupied 38.5% of the total area of the Province. The amount of oxygen release in the reforested croplands increased by 1.43×10⁷ t·a^-1, and the oxygen release value totaled 5.053 billions Yuan. In the reforested croplands, the carbon fixation density had a slow increase (though with fluctuation), but the increasing trend was more significant and the increment was higher than that in the perimeter zones. The area where the carbon fixation density increased occupied 99.8% of the reforested cropland area, while the area where the carbon fixation density decreased only occupied 0.2%. The proportion of the total area with low carbon fixation density was decreasing, while that with medium and high carbon densities was increasing. In the reforested cropland area, the carbon fixation density in the main land-use types had an obvious increasing trend, while that in different steep lands showed different increasing trend, being most significant (P<0.01) in>25° lands. It was suggested that with the implementation of the project of reforesting cultivated land, vegetation coverage improved gradually, and significant benefits were obtained from the carbon fixation and oxygen release in reforested cropland area.