A cooperative treatment method for dioxin and heavy metal in flying ash on the basis of steel slag and mineral slag is characterized by comprising the following steps that (1) to-be-treated flying ashand a dehalogenation agent are mixed according to a mass ratio of 4:1-9:1, mixed milling is conducted by a planetary mill or a ball mill, and after 2-10 h of continuous ball milling, organochlorine degradation flying ash is obtained; (2) the organochlorine degradation flying ash and a curing agent are mixed according to the mass ratio of 4:1-9:1 and are stirred evenly, and a flying ash mixture isobtained; and (3) water or a reducing agent of the mass ratio of 15% is added into the flying ash mixture, the obtained mixture is put into a compaction die for compaction forming, pressure is 20-50kN, pressing time is 15-30 s, maintenance is conducted for 3-7 days, and a flying ash solidified body is obtained. Through the cooperative treatment method, dioxins and heavy metal pollutants can be treated simultaneously, steel slag serves as a main material of the dehalogenation agent and can be utilized efficiently, and the problem of a low comprehensive utilization rate of the steel slag is solved while the flying ash is treated.