The invention discloses a complex coagulant for advanced treatment of biochemical 
tail water, and its preparation method and application. The complex coagulant is characterized in that the complex coagulant is an 
inorganic polymer complex coagulant prepared form 
industrial waste or nonmetallic mineral materials as main materials under heating conditions through the processes of 
alkaline hydrolysis, acid leaching oxidation, hydrolyzation and 
polymerization; and the complex coagulant prepared by the preparation method contains 20 to 35% of 
silicon, 15 to 25% of aluminum, 6 to 11% of iron and 3 to 6% of 
boron. Compared with the prior arts, the preparation method has the advantages of easy acquirement of raw materials, simple process, and good economical efficiency and applicability. The 
inorganic polymer complex coagulant prepared by the preparation method has the advantages of good performances of adsorption and bridging, 
charge neutrality, bonding and gathering, and decoloration, big flocs, fast 
sedimentation velocity of flocs, and low use amount. The complex coagulant can be widely utilized for the field of 
wastewater treatment, and is especially suitable for advanced treatment ofbiochemical 
tail water.