In this paper, Landsat-8 OLI images were combined with Sentinel-2 images, and the Fraction of Photosynthetic Active Radiation (FPAR) was used to construct the pixel-by-layer correction factor that was applied to improve the spatial resolution of the MODIS Gross Primary Production (GPP) images. Based on this, the vegetation growth status before and after the improvement of saline-alkali farmland was studied in Zhaogui Gedan formation in Bayannur City, the Inner Mongolia. At the same time, combined with the data of soil salinity at different depths, this paper used the transfer matrix method and hot spot analysis method to study the global changes in soil salinity and the local differences in changes of vegetation growth. The results showed that:(1) the most obvious improvement effect of soil salinity was found in the plots 12-20, and the improvement effect gradually decreased with the increase of soil depth. In the soil depth 0-20 cm, the conversion area of the saline soil to the moderately saline soil was the largest; In the soil depth 20-40 cm, the conversion area of the severely saline soil to the moderately saline soil was the largest; In the soil depth 40-60 cm, the area transferred in of the severely saline soil and the saline soil was larger than the area transferred out, while the area transferred in of the other soil types was smaller than the area transferred out. (2) The lifting area of GPP was about 603.6 thousand m² more than the lowering area, accounting for 42.88% of the study area. Meanwhile, the improvement effect was more obvious in the area with low GPP before improvement. (3) The hot spots in the lifting area of GPP were concentrated in the plots 12-17, 25-27, and 34, indicating that the improvement effect of this area was significant. The cold spots in the lowering area of GPP were concentrated in the plots 6, 12-14, 22-23, 27-28, and 30-31, indicating that the improvement effect in this area was poor.