A boron-containing polysilicate aluminium manganese flocculant was prepared with sodium silicate, aluminium sulfate, manganese sulfate and sodium tetraborate as raw materials, and applied to the treatment of Songhua River. The results showed that under the conditions of n (Al): n (Mn) = 8:2, n (B): n (Si) = 0.15, n (Al): n (Si) = 0.8, constant temperature heating temperature of water bath at 40℃, and pH 2.5, the new boron-containing polysilicate aluminium manganese flocculant had the best flocculation effect on Songhua River, and its color removal rate could reach 96.23% and turbidity removal rate could reach 95.81%.