To understand changes in the ecological environment and its main driving forces in the ecologically fragile areas of the Loess Plateau in the past 20 years since the implementation of the "Grain for Green" Program, taking Yulin City as a typical example of the fragile ecological environment on the Loess Plateau, The vegetation coverage of Yulin City from 2001 to 2020 was estimated based on the pixel dichotomy model. This study analyzed the spatial and temporal variations of the vegetation coverage in Yulin City during the past 20 years by using univariate linear regression methods. The dominant factors affecting the interannual changes and spatial distribution of vegetation coverage were analyzed by using the partial correlation analysis and geographic detector methods during the different periods of "Grain for Green" Program. The results showed that:(1) The vegetation coverage in Yulin City significantly increased with time series (S=0.011, p<0.01) from 2001 to 2020. The vegetation coverage during the construction period (2001-2010) increased significantly (S=0.013, p<0.01), while its increasing trend in the consolidation period (2011-2020) was not significant (S=0.005, p>0.05). (2) The spatial distribution of vegetation coverage in Yulin City decreased from east to west from 2001 to 2020. The vegetation coverage of all counties (districts) in Yulin City showed an overall increasing trend, among which the eastern part of Yulin City had a more significant growth trend. However, the proportion of area with increasing vegetation coverage in Yulin City in the construction period (82.1%) was larger than that in the consolidation period (58.0%). (3) From 2001 to 2020, the dominant factors affecting inter annual change of vegetation coverage were the cumulative area of the Grain for Green Program and rainfall. The cumulative area of the Grain for Green Program was the primary factor in the construction periods, while rainfall was the primary factor in the consolidation period. (4) Soil texture, rainfall and land use type mainly affected the spatial distribution of vegetation coverage from 2001 to 2020. During construction and consolidation periods, the spatial differences of soil texture were closely related to spatial stratified heterogeneity in the vegetation coverage. The spatial heterogeneity of vegetation distribution and the interaction between the main influencing factors could provide a scientific basis for the precise implementation of ecological restoration measures.