Based on the samples data, 6 factors to form an assessment index system were selected and art assessment model of ecological fragile degree with the euclidean distance formula was established. The weights of factor were calculated through respective apparent and recessive Karst types using the method of stratification analysis. Result showed that vegetation and area of bare-rock had more weight and effects among 6 indexes. According to the calculated results of ecological fragile degree, frangibility of 64 samples was assessed and divided into 5 grades, which were slight(≤0.2), light(0.21～0.4), medium(0.41～0.60), strong (0.61～0. 80) and ultra strong(>0. 80). The result also showed that the geologic background was frangible essential to Karst environment and its frangibility degree of environment was decided by vegetation status if other conditions were the same.