The invention discloses porous magnetic ceramsite based on municipal sludge and a preparation method and application thereof. The porous magnetic ceramsite is prepared from the following components inparts by weight: 100 parts of municipal sludge, 6-10 parts of bauxite, 4-8 parts of diatomite, 2-6 parts of fly ash, 0.01-0.1 part of cyclopentadienyl iron, 1-2 parts of magnesium lithium silicate, 0.1-1 part of ferric nitrate, 0.1-0.3 part of cobalt nitrate, 0.1-1 part of nickel nitrate, and 1-3 parts of a pore-making agent; the preparation method includes the following steps that (1) the municipal sludge, the bauxite and other raw materials are dipping-cooked by acid; (2) the PH is adjusted to 8.4-9.2 by ammonium hydroxide, and ageing is conducted by adding nitrate; (3) a ceramsite raw material is prepared; and (4) the ceramsite is sintered. According to the porous magnetic ceramsite based on the municipal sludge and the preparation method and application thereof, the porous ceramsite loaded with magnetic nano Fe<2>O<3>/Co<3>O<4>/NiO is directly prepared by adopting a one-step method, advance dipping of a composite precursor solution of an iron salt, a nickel salt and a cobalt saltdoes not need to be adopted, the method is simple, operation is convenient and quick, the load is higher, the porous magnetic ceramsite is suitable for large-scale industrial production, at the same time, nanoparticles can be distributed stably in the ceramsite network structure, a homogeneous system is formed, and layering and shedding of the nanoparticles are avoided.