Quick lime has been widely applied for improving strength and water stability of loess due to its lower costs and better effect on subgrade construction. Taking collapsible loess of Dingxi section of Luoding Freeway in Gansu province as investigation object, CBR were done in cases of different quick lime contents, water contents and compaction times as well as immersion times. The results indicated that compaction degree of lime soil would be lower than that of loess as subjected to the same compaction times. The strength and water stability of loess mixed with quick lime would obviously improve. The optimal quick lime contents were equal to 3%. A dual linear regression equation of CBR was put forward and applied in six test sections of Luoding and Baotian freeways.