The invention relates to fly ash coated sludge ceramsite and a preparation method therefor. According to the fly ash coated sludge ceramsite, sludge serves as a main raw material, shale, feldspar powder and a foamer serve as auxiliary raw materials, and the mixed amount of dry sludge in the raw materials of the ceramsite is 35.0-58.0wt.%. The preparation method comprises the steps of firstly accurately weighing the dry sludge or wet sludge with certain moisture, the shale, the feldspar powder and the foamer according to a designed ingredient proportioning ratio, then, carrying out uniform mixing, granulating the mixture, coating the surface of each unburnt sludge ceramsite with a layer of fly ash, meanwhile, adding a certain volume of fly ash into a rotary kiln, then, carrying out foaming burning on the fly ash coated unburnt sludge ceramsites, and carrying out annealing cooling, thereby obtaining the sludge ceramsite. According to the fly ash coated sludge ceramsite and the preparation method therefor, the ceramsite is prepared by taking the sludge as the main raw material; due to fly ash coated sludge ceramsites, the mutual adhesion among the ceramsites in a dynamic burning process can be effectively prevented, so that the rate of final ceramsite products is increased; and meanwhile, the utilization of the sludge of sewage plants is developed towards a harmless, volume-reducing and resource-converting direction, so that the fly ash coated sludge ceramsite and the preparation method therefor have remarkable economic, environmental and social benefits.