To construct an automatic discrimination method for the causes of pavement diseases, the typical characteristics of different types of asphalt pavement diseases of the Inner Ring Expressway in Chongqing, which was taken as an engineering example, were analyzed, and the feasibility of data dimension reduction analysis was determined based on the correlation characteristics of different types of damage. Then, numerous state information data were subjected to dimension reduction through the principal component analysis (PCA), followed by the automatic cause analysis of pavement diseases using the random forest algorithm. The results show that the cause conclusions acquired through machine learning model training basically accord with the actual field survey conclusions. Thus, it can be deemed that the intelligent discrimination method based on machine learning is reliable, to some extent, for the cause analysis of pavement diseases and can serve as an automatic discrimination method for the follow-up development of an intelligent maintenance decision system.