Abstract: Soluble carbonate rocks in karst or karst phenomena is a natural geological phenomenon. In South Southwest of China, the geological conditions of terrain are complex, and distribution of karst terrain is widely observed. It is difficulty to build highway road in these areas. The mode is approximately simplified by structural mechanics to quantitatively calculate the stability of the highway embankment in karst areas. It gives the relationship of stability between cave roof, span, and cover depth. It is a certain model. It has some reference value for stability analysis and evaluation of highway embankment in the future.