The water resource pollution was serious all over the world. The main sources of drinking water such as rivers and lakes were contaminated by large amounts of industrial and urban wastewater. Therefore, effective treatment of sewage was urgent. Flocculation was the most widely used method in water treatment technology. The choice of flocculants was the most critical step in dealing with the polluted water. The application of inorganic, organic, microbial and composite flocculants in water treatment were discussed in this paper. The advantages and disadvantages were analyzed, respectively. The development prospects of four flocculants in the field of water treatment were investigated.