Crowd analysis becomes the most active-oriented research and trendy topic in computer vision nowadays. Within the crowd, there exist many behavior anomalies or abnormalities. There are many ways of detecting these abnormalities such as crowd density estimation, crowd motion detection, crowd tracking and crowd behavior recognition. The abnormal behaviors of crowd are analyzed, and the three key features of abnormal crowd are summarized. The feature extraction, anomaly identification technology, anomalies classification and databases of the crowd are respectively summarized, and the current problems, as well as the suggestions and comments about the future direction of research are then proposed. Article has a certain reference value for the research in related fields.