Abstract: The problems of karst collapse can't be overlooked to engineering construction. The paper studies the extent of the karst collapse degree of two main factors(impact load and underground water) in high-speed of Guangzhou to Qingyuan. Based on data collection and field research, it concludes 12 points' basic information of karst collapse in research area, and sum up the characters of collapses and main effective factors. Besides, it sets up the geological model of sandy soil silty clay limestone,which conforms with the actual structure of overburden. In addition, it calculates the stability coefficient of overburden under two conditions using the limit equilibrium theory. It turns out the maximum impact loads.