Using Image-Pro plus software, we analyzed the SEM images and extracted the features of flocculation, such as the diameter, pore diameter, porosity, and void ratio. We also analyzed the relationships between the features mentioned above and sand concentration, and between these features and flocculant concentration. The results of flocculation characteristics variation laws using the Image-pro plus software were consistent with the existing conclusions, and flocculation setting velocity decreased with the increasing void ratio. Therefore, the Image-pro plus software can be applied to analyze the SEM images of flocculation.