The invention discloses a method and system for co-processing waste incineration fly ash through a rotary hearth furnace, and the system for co-processing waste incineration fly ash through the rotary hearth furnace comprises a material mixing machine, a ball press machine, a drying machine, the rotary hearth furnace, a waste heat boiler and a dust removal device.The method comprises the steps that after ferrous metallurgy dust and mud, waste incineration fly ash, a binder and water are evenly mixed, the mixture is heated to the room temperature; the method comprises the following steps: firstly, preparing a metal pellet, pressing into pellets to obtain carbon-containing pellets, then drying the carbon-containing pellets, feeding the carbon-containing pellets into a rotary hearth furnace, carrying out reduction roasting to obtain metallized pellets and zinc-containing flue gas, and then carrying out heat exchange and dust removal on the zinc-containing flue gas to obtain zinc-containing dust. According to the method, the waste incineration fly ash and the ferrous metallurgy dust sludge are cooperatively treated in the rotary hearth furnace, the dezincification rate and the metallization rate of the ferrous metallurgy dust sludge are increased through the waste fly ash, the using amount of a binder is saved, the cost is reduced, meanwhile, the content of dioxin in the waste incineration fly ash is reduced, and the environment friendliness is achieved. And harmless treatment and resource utilization of the waste incineration fly ash and the ferrous metallurgy dust sludge are achieved.