Conducting a diachronic study of vegetation cover helps to assess its transformations over a period of time, allowing for a comprehensive assessment of the factors influencing these transformations. The purpose of this research is to analyze the vegetation cover spatio-temporal changes within Beni Haroun watershed, located in the northeast region of Algeria. Based on remote sensing data, two satellite images from Landsat 7 ETM+ and Landsat 8 OLI/TIRS were downloaded for the years 2009 and 2020. The Normalized Difference Vegetation Index was employed to remotely detect and monitor the changes of the vegetation cover. It was calculated for both chosen dates, and the results were classified into four classes (no vegetation, sparse vegetation, moderate vegetation, dense vegetation), each representing a different vegetation density. The obtained maps showed a regression of the vegetation cover. The NDVI values have decreased from 0.77 in 2009 to 0.58 in 2020. Spatial patterns in the classified NDVI maps illustrated reduced vegetation cover demonstrated by an expansion of the no vegetation class 353479 ha in 2009, 567916 ha in 2020. The final map of the change detection depicted a predominance of the negative change throughout Beni Haroun watershed, in consequence of various controlling factors, including climate and human interventions.