Landslides and collapses on mountain massifs with thick layered limestone masses distribute widely in mountainous area in southwestern China. It is of important significance for risk assessment and prevention to study the failure patterns and their formation mechanisms of this kind geohazards. Based on detail field investigation, the development features, failure patterns and their formation mechanisms of the large perilous rocks in the area of Yangjiaochang Town in Wulong County, Chongqing City are studied in this paper. Main conclusions are as follows: there are 11 large perilous rocks at the abrupt cliff in the Yangjiaochang Town area, with the total volume nearly 1280×104m3. According to the shapes, features of main structural planes and signs of deformation, the failure patterns can be divided into four types which are apparent dip slide, slide collapse, topple and rockfall; The main influence factors are slope structure, lithological combination, rock mass structure, karstification and mining activities etc., This study discusses the mechanism affecting formation of the perilous rocks in detail.