The Grain for Green Project (GGP), one of the most ambitious ecological projects to be launched in China, was aimed at converting low-yield slope cropland, barren hills, and wasteland into grassland and woodland. The objective of this study was to calculate the carbon stock changes and carbon sequestration potential of the GGP in Western Henan under cutting and no-cutting scenarios, in order to develop a method for further estimation of the carbon sequestration potential of the national GGP and produce a scientific reference for the ecological system management of the GGP in the long run. The Western Henan, one of the major districts that implemented the GGP in China, initiated the GGP in 2002. We analyzed Songxian, which is a major county in terms of implementation of the GGP in Western Henan, as a case to evaluate carbon storage and the carbon sequestration potential under cutting and no-cutting scenarios. We collected data on each year from 2002 to 2010, such as tree species, the planted area of the project in Songxian, the use of a growth curve suitable for China's planting volume, the findings about the soil organic carbon changes after the GGP together with biomass density of various species, carbon content, the biomass expansion factor, and the estimated carbon storage and annual carbon sequestration for the GGP from 2002 to 2050. The results showed that total carbon storage was 0.470 Tg in 2010, when the project was completed. Total carbon sequestration in the former period is larger than that in the latter period during the project's implementation. The annual carbon sequestration of the soil organic-carbon pool was negative and released carbon from 2002 to 2010, then an increase in the annual carbon sequestration of soil organic-carbon pool was observed, along with net carbon gains after 2011; the project's annual carbon sequestration peaked in 2015 under no-cutting and cutting scenarios. The annual carbon sequestration under the cutting scenario is greater than that under the no-cutting scenario after 2033. The potential increment of the carbon sink of the GGP-covered Songxian will reach 0.760, 1.464, 1.852, and 1.985 Tg by the year 2020, 2030, 2040, and 2050 under the no-cutting scenario; it will reach 0.760, 1.240, 1.657, and 2.000 Tg under the cutting scenario. The potential increment of the carbon sink under the cutting scenario will exceed that of the no-cutting scenario after 2050. In the long run, the GGP in Western Henan has a greater carbon sequestration potential under the cutting scenario than that under the no-cutting scenario. Our results suggest that moderate forest harvesting for the GGP can increase the capacity for carbon sequestration.