Abstract: Loess collapse is the common disaster in loess area, and influences the safety of human's life and production. According to the survey on site, it is believed that the main internal causes of loess collapse formation are the characteristics of loess soil and the joint cutting level, and the main external causes are the function of rainfall, human activity and biological activity. In terms of the common form of movement for loess collapse, the theory formula that determines the range of collapse body is presented under the condition that the collapse body falls freely and rolls. The example calculations show that, at the base of the ground level, no matter what the movement it is,the influence range of collapsing is 0.4～0.6 times of the slope height. As the slope steepens, the ratio for sliding distance and the slope height is enlarged accordingly. When the collapse body falls freely, the influence range of the collapse body has a relationship with the gradient of the collision point. When the collapse body slides in the slope, the influence range of collapse body has a relationship with the degree of slope. Research results can be used as the forecasting methods for the disaster range caused by loess collapse in loess area, which provides the theoretical basis for preventing loess collapse.