The invention provides a preparation method of a biological purifying carrier for treating wastewater. The preparation method comprises the following steps: mixing pretreated attapulgite with MBAA (Methylene Bisacrylamide) in brine and stirring at the temperature of 50 to 70 DEG C for 1 to 3 hours; mixing a biopolymer solution with a mixed solution, heating the solution to 40 to 60 DEG C, adding activated sludge of which the mass is 2 to 5 percent that of the attapulgite and 1 to 3 percent of nano-iron manganese composite oxide, adding a carbon nano tube of which the mass is 2 to 5 percent ofthat of the attapulgite, and carrying out stirring treatment at the stirring speed of 5 to 10 rounds/min for 1 to 3 hours; then adding a cyclodextrin complex solution into the mixed solution, and stirring at the temperature of 20 to 30 DEG C for 20 to 40 minutes; standing at the temperature of 10 DEG C for 30 minutes, adjusting the temperature to 5 DEG C below zero to 7 DEG C and keeping for 40 to60 minutes; slowly stirring, curing and crosslinking, wrapping a mixture with gauze, then extruding out water, and flushing the mixture by using 10 to 20 percent tannic acid solution for 2 to 3 times; putting the mixture into a baking oven with the temperature of 50 to 70 DEG C and treating for 8 to 10 hours, thus obtaining a finished product. The preparation method of the biological purifying carrier for treating the wastewater, disclosed by the invention, has the advantages that the efficiency and the ability of sewage treatment can be effectively improved.