Abstract: Loess collapse is a type of very common geological disasters in the loess plateau area of Northwest China.At first,this paper studies loess topography,loess type and structure,loess vertical joints,slope erosion,rainfall and human activities.The results show that both the vertical joints in loess and erosion at the toe of slope are the main causes of loess collapse.Secondly,based on field investigation and analysis on the geological phenomena,four typical failure modesare put forward to describe different types of loess collapses.They are tensile crack-falling,tensile crack-toppling,tensile crack-subsiding and tensile crack-sliding.By means of discrete element method,a typical loess slope of Heilonggou is simulated.The failure process of loess collapse includes erosion flaking,local recessing,vertical joints opening,drop breakup,accumulation at the toe of the slope.Research findings in the paper are significant to prevention and treatment for loess collapse in the loess plateau area of Northwest China.