本文介绍了絮体等效直径与沉淀水浊度的相关性，提出利用絮体等效直径进行混凝控制的方法和基于最大方差比的矾花图像分割算法。实际应用表明，该技术取得了很好的控制效果，具有广阔的应用前景。关键词：等效直径；方差比；混凝控制Abstract: This paper presents the relativity between the equivalent diameter and turbidity of settled water, proposes a method of coagulation control used the equivalent diameter and an alum image segmentation algorithm based on the maximal variance ratio.The application shows that the method can obtain satisfactory control,and has broad application foreground.Keywords: equivalent diameter;variance ratio;coagulation control