Terrestrial carbon storage is an important indicator of ecosystem carbon storage services, and it has a close relationship with land use change. The Green for Grain Program (GFGP) has brought about great changes in the pattern of land use in the region and had a major impact on ecosystem carbon storage services. In order to simply and quickly assess the impact of GFGP on terrestrial ecosystem carbon storage services, this paper takes Zichang county, which is located in the hilly and gully region of the Loess Plateau, as an example, and used InVEST model to assess the impact of GFGP on the carbon storage of terrestrial ecosystems. Moreover, by coupling InVEST model and FLUS model, according to the set A, B, C, and D scenarios of GFGP, the change of terrestrial ecosystem carbon storage and the economic value of carbon sinks in Zichang county in 2037 were predicted. The study found that: (1) Remarkable effect of GFGP in Zichang county occurred. From 2000 to 2017, a total of 31627.98 hm2 of cultivated land was converted to woodland and grassland. The forest and grass coverage rates in the study area increased from 53.26% in 2000 to 64.20% in 2017. (2) The carbon storage service of the terrestrial ecosystem was significantly improved from 2000 to 2017. The terrestrial carbon storage increased from 39.19×106 t in 2000 to 42.34×106 t in 2017, and its growth was mainly found in the main stage of project implementation from 2000 to 2008. (3) In the future, it is assumed that the GFGP will continue to be implemented in the county, and its ecosystem carbon storage services will be further improved. In addition, certain carbon sink economic value will be obtained. Until 2037, it is expected that the terrestrial carbon reserves under the four scenarios of GFGP in the county will reach 43.78×106 t (GFGP scenario A), 44.10×106 t (GFGP scenario B), 44.32×106 t (GFGP scenario C) and 44.54×106 t (GFGP scenario D), respectively. Thus, the net income from the economic value of carbon sinks was US$ 1627.88 million, US$ 1979.89 million, US$ 2231.39 million and US$ 2471.67 million, respectively. The coupled InVEST-FLUS model can not only use the InVEST model to evaluate land carbon stocks simply and quickly, but also calculate the terrestrial carbon reserves and carbon sink economic value under future land use change scenarios based on the FLUS model.