The invention discloses a physical chemistry method for changing a fragile ecological environment in a loess area and increasing arable land. The method includes the steps of 1, conducting bulldozing leveling on loess hills, table land and ridges which need to be improved; 2, measuring the compactness, permeability coefficient and moisture content of loess before improvement; 3, destructing columnar jointing of the loess through dynamic compaction of a dynamic compaction machine, and eliminating subtle channels which make water permeate downward and are produced by columnar jointing; 4, sprinkling a grouting material on the loess after the dynamic compaction, wherein the grouting material permeates along the vertical columnar jointing of the loess, and the grouting material expands and solidifies rapidly when permeating into a predetermined position under the earth surface and thus blocks the vertical columnar jointing; 5, detecting the permeability, compaction degree and moisture content of the improved loess, and determining plants which can be planted. The physical chemistry method has the advantages of effectively preventing soil and water loss in the loess area, changing the soil microstructure, making the water conserved in the soil structure, and effectively improving the fragile ecological environment in the loess area.