The invention discloses a double-layer compound 
biological filter material for an aerated 
biological filter. The double-layer compound 
biological filter material is formed by combining an inner layer and an outer layer, wherein the inner layer consists of attapulgite clay and 
fly ash in a weight ratio of 4:6; and the outer layer consists of attapulgite clay, kieselguhr and 
coal dust in a weight ratio of 7-10:9-12:1. The preparation method comprises the following steps of: uniformly mixing the attapulgite clay and the 
fly ash, and forming inner cores of 
solid spheres in a granulator; uniformly mixing the attapulgite clay, the kieselguhr and the 
coal dust to obtain mixed 
powder, continuously and slowly adding the mixed 
powder into the granulator to coat the surfaces of the inner cores of the 
solid spheres for 
granulation to obtain the finished product spheres; and 
drying the finished spheres naturally for 24 hours and in a constant-temperature fan 
drying box at the temperature of 120 DEG C for 2 hours, taking the finished spheres out of the 
drying box, directly putting the finished spheres in a box-typed resistance furnace to sinter the finished spheres at the temperature of between 950 and 1.050 DEG C for 20 minutes, and naturally cooling the finished spheres to obtain the double-layer compound biological 
filter material. The double-layer compound biological 
filter material obtained by the preparation method has the advantages of 
rough surface, high 
void ratio, good wearing resistance, high strength, easy film formation and high economy and practicability.