For studying the effect of the property of polyacrylamide on flocculation efficiency, nonionic polyacrylamide of coal slurry, compose anion polyacrylamide and cation polyacrylamide of coal shurry and make flocculating settling experiments on the discharge of Wangfenggang Coal Preparation Plant. The influence of molecular weight, hydrolytic degree (HD) and cationic degree(CD) on flocculation efficiency wiss researched, and flocculation mechanism of polyacrylamide are also analyzed.