By much field investigation and research, we find there are many different types of cracks and fissures in loess and they form cracks and fissures network. These cracks and fissures are structure planes of dividing loess, preponderance planes of tunnel erosion of soil, control planes of arising geological hazards and are seeping channels and storing room of groundwater. So to study on them is very important and useful. The cracks and fissures have been classified according to their size, character of mechanics, cause and time of formation. Affected by neotectonics, landform, groundwater and climate in Loess Plateau of China and by character, structure, component, granularity, age and depth of loess, characteristics and distribution of cracks and fissures of loess in Loess Plateau are different and are summed up here. We consider the commonly vertical joints in loess as to be growing up from some of the different original and secondary vertical cracks during sedimentation of loess.