Abstract: Loess discontinuous surfaces can be collectively called the loess interfaces. They are generated by the nature environment and human engineering activities. The loess interface is the basic controlling factor of loess catastrophe. Based on the interface disaster effect, the loess interface is divided into megainterface, macrointerface, mesointerface and microinterface. The loess mesointerface refers to the discontinuous surface that divides the loess block. We conduct extensive field investigation to enhance the understanding of loess mesointerface. According to the investigation statistical results, we propose the geometric features of the mesointerface with round shape, hook shape, pinch-out shape, and V shape. The combined features include claw shaped, step shaped, feather shaped, and grids shape. Based on the cause mechanism, the mesointerface is classified as physical mechanics, biological activities, water-soil interaction, weathering, and heterogeneous. The loess meso interface has a hazard-induced effect of separation, loosening and seepage softening on soil. The preliminary research on loess mesointerface would provide scientific reference for studying the loess catastrophe mechanism.