China's mountainous terrain is widely distributed，and the collapse of mountainous dangerous rocks is one of the major geological disasters in mountainous areas.In order to study the influence of different crack angles，horizontal seismic forces and vertical seismic forces on the safety factor of dangerous rock mass，the maximum circumferential stress criterion is used to deeply cut the“V” type valley of the Chishui river in the intersection of Guizhou plateau and Sichuan basin.The stability analysis of the dangerous rock mass leads to the conclusion that the safety factor of the dangerous rock body decreases with the increase of the crack angle，but when the crack angle is less than 55°，the safety factor of the dangerous rock mass decreases rapidly，and the crack When the angle is greater than 55°，the safety factor decreases slowly；the safety factor of dangerous rock mass decreases with the increase of horizontal seismic coefficient or vertical seismic coefficient， and it decreases linearly； the damage of horizontal seismic force to dangerous rock mass.The degree is higher than the vertical seismic force of equal size.