A large number of earthen sites are found in arid and semi arid regions of Northwest China. Based on the field investigation of earthen sites in Northwest China, this paper summarizes the diseases of these sites in the study area according to the types of disease causes. The quantitative fitting analysis of survey data revealed an internal relationship between four typical diseases, namely cracks, erosion, gullies, and collapse, and a sequence and promotion relationship between the formation and development of various diseases. Linear fitting results show a positive correlation among the four aforementioned diseases in varying degrees; cracks, erosion, and gullies will eventually lead to the collapse of earthen sites. The correction coefficient indicates that the most significant factors leading to the collapse of earthen sites are the development of gullies and erosion. Thus, the reinforcement and protection of earthen sites should consider a variety of diseases, and comprehensive treatment of multiple diseases should be performed to delay the destruction of earthen sites to the largest extent.