Abstract: Regional ecological security has been paid more and more attention, and it’s of special significance to study the ecological security and its driving factors in ecological fragile areas. In this paper, the ecological security and its driving factors in typical fragile regions in Loess Plateau were analyzed at district and county scales. Yulin District and Hengshan County were taken as the cases, and ecological security index system was constructed to assess the security levels of the two regions. By using AHP method, the spatial differentiation of ecological security at different scales was studied, and the results showed that there existed differences among the twelve counties in Yulin District, with the security level being generally higher in southwest and lower in northeast. Similar tendency was observed in Hengshan County, with the security level being lower in north and northeast, and varying among different scales in southwest. Climate and topography were the weak driving forces, while human disturbances had great influence on ecological security.

Key words: Citric acid, Oxalic acid, Pb, Cd, Soil chemical behavior