Abstract: In order to investigate the main components and toxicity of fly ash attached with deactivated denitrification catalysts in coal-fired power plants, fly ash sample was collected, and a series of characterization analysis(XRF,XRD and SEM) was carried out on the fly ash.Meanwhile, the leaching toxicity of heavy metals in fly ash was investigated with sulfuric acid and nitric acid leaching method.The results showed that the main components of fly ash were silicon dioxide, aluminosilicate and calcium sulfate.And a certain amount of titanium dioxide was in fly ash.Some heavy metals(copper, zinc, chromium, lead, barium and nickel) were detected, and the content of nickel, arsenic and vanadium were 66.96,252.33 and 432.85 mg/kg respectively, which were higher than other metals.The leaching toxicity of heavy metals in fly ash was conducted with the sulfuric acid and nitric acid leaching method.The elements copper, zinc, chromium, lead, barium and nickel in the fly ash were considered, and the leaching amounts were 0.042,0.038,0.011,0.006,0.004 and 0.034 mg/L respectively.At the same time, it was found that the leaching amount of arsenic in the fly ash was 9.33 mg/L,which was higher than the standard 5 mg/L,and the vanadium content in the leaching solution was as high as 27.27 mg/L.It showed that fly ash has certain leaching toxicity.In order to reduce the leaching toxicity of vanadium and arsenic in fly ash, sodium hydroxide solution was used to leach vanadium and arsenic in fly ash.The influence of alkali concentration, temperature and alkaline leaching time on the leaching efficiency of vanadium and arsenic in fly ash was investigated.The leaching rates of vanadium and arsenic can reach 99.24% and 92.33% respectively at the best conditions(sodium hydroxide concentration 11%,leaching temperature 70 ℃,and leaching time 60 min).The leaching toxicity of vanadium and arsenic from the leaching residue was also conducted.The leaching amount of vanadium and arsenic decreased to 0 with the sulfuric acid nitric acid leaching method, meanwhile, the leaching amounts of other metals were reduced greatly.Vanadium and arsenic in the leaching solution can be used for subsequent resources.