Most forests in Azerbaijan are distributed in mountain ecosystems, and lowland forests cover very small area. The biodiversity of these lowlands has faced the danger of depletion over the last 100 years. From this point of view, a comprehensive study of the forests of the Samur-Yalama National Park is of special importance. Initially, it is expedient to study the changes of vegetation cover, which later will allow us to investigate reasons for the formation of stressful areas. Normally there is a high correlation between changes of the chlorophyll content of the vegetation and their health, density, stress, and photosynthetic processes. Chlorophyll content was studied by using Chlorophyll Index green algorithm. Multispectral images were obtained from the Landsat 5 TM and 8 OLI program of the USA for 1989-2019 years. The best indicators of chlorophyll content were observed in June. During 30 years, the forest cover density with high chlorophyll content (on index 3) decreased from 765 ha to zero. In general, there is a reduction of about 12% in the density of forest cover. Although there is a decrease in agricultural areas (on 0 index), which is related with the rapid shift of interest to horticulture and increasing of the forest plantations in the last years.