During the construction of Heda expressway, the Ermi landslide, which occurred on section K377, has interrupted the construction of the expressway. Additional engineering geological investigation became necessary. The direct economic losses are over 3 million US dollars. This paper analyzed the Ermi landslide from the aspects of formation process, engineering geological conditions, the structural characteristics and stability analysis of the landslide. The results show that the formation of the Ermi landslide is mainly due to geological conditions in project area. Because the structure of the sliding body is loose and some weak interlayer exists in the slope, the shear strength of the sliding surface and sliding body is low. As cut-slope excavating, the resistant of the slope body reduced. Eventually the slope lost its stability and a landslide formed. In the stability analysis of the slope, the shear strength parameters of the sliding surface was determined by anti-analysis. Therefore, the result of the evaluation is closer to the actual conditions. Analyzing the stability of the three sliding surfaces respectively, the stability factors for initial slope are between 1.211 and 1.468, and the stability factors for current slope are between 0.958 and 1.076. Hence, the cut-slope excavation is the direct cause of the landslide.