As a fragile ecological environment area in China, the former concentrated contiguous impoverished areas is the main battlefield for returning farmland to forests and grasslands. Its effect of returning farmland to forests and grasslands directly reflects the overall effect of the implementation of the project of returning farmland to forests and grasslands, whicht provides a mirror of the experience of consolidating and expanding the results of returning farmland to forests and grasslands in the new journey. Taking 14 concentrated contiguous impoverished areas specified in the document "China’s Rural Poverty Alleviation and Development Programme (2011-2020)" as the study area, based on the 2000-2020 ecosystem annual gross primary productivity (AGPP) dataset and the normalised vegetation index (NDVI) dataset, we compared and analysed the inter-annual changes in the AGPP and NDVI of fallowed and un-fallowed areas in the concentrated contiguous impoverished areas, in order to assess the ecological effect of implementing the project of returning farmland to forests and grasslands in the concentrated contiguous impoverished areas. The study found that: (1) from 2000 to 2020, the area of returning farmland to forests and grasslands in the concentrated contiguous impoverished area was 178554 km², accounting for 44.71% of the total area of arable land in 2000. (2) During the study period, AGPP and NDVI in the fallow and non-fallow areas showed an overall increasing trend, with 69.07% and 86.51% of the total area in the fallow area showing highly significant and significant increasing trends in AGPP and NDVI, respectively, while the proportion in the non-fallow area being 65.88% and 72.61%, respectively. The annual mean and relative rate of change of AGPP and NDVI were higher than those of the non-returned farmland area. (3) From 2000 to 2020, the inter-annual trends of AGPP and NDVI in the whole region, the fallow area and the non-fallowed area were generally consistent, showing a linear increasing trend. The growth of AGPP and NDVI in the fallow area was always higher than that in the whole of the concentrated contiguous impoverished area and the non-fallowed area. Therefore, this study provides a reference basis for further adjusting and optimizing the policy of returning farmland to forest and grassland by exploring the impacts of returning farmland to forest and grassland in the former concentrated contiguous impoverished area on AGPP and NDVI.