The physical and chemical properties of biomass after torrefaction can be significantly improved,which enable the biomass to replace coal in large scale for power generation and CO2 emission reduction. However,ash deposition and corrosion during the combustion are still urgent issues to be solved,and systematic investigations on the influence of torrefaction on the corrosion behavior of biomass combustion is rarely available. In view of this,two typical biomass,corn stalk and wheat straw,were selected to prepare their torrefied samples in a fixed-bed reactor,and the effects of torrefaction on the occurrence modes and contents of key ash-forming elements in the biomass were investigated through chemical fractionation analysis combined with ICP-MS and IC tests. Combustion tests of biomasses,two typical power coals and the blends of biomass and coal were conducted on a drop-tube furnace,and the bulk ash was collected. 12CrMoVG steel was selected as tested alloy for corrosion tests which conducted on a horizontal tube furnace at 550 ℃. The corrosion behavior of loading ash from individual combustion under atmosphere containing HCl,and loading ash from co-combustion under atmosphere containing HCl and SO2 were investigated. The mass increment of ash loaded-alloys after corrosion tests were weighed. The morphology and composition characteristics of the corroded samples were analyzed by SEM-EDS. Finally,the influence of torrefaction on the corrosion propensity of co-combustion of biomass and coal was revealed through corrosion tests under atmosphere with various HCl concentrations. The results indicate that the corn stalk and wheat straw contain considerable amounts of Cl and K. After torrefaction at 270 ℃,17.84% and 38.76% Cl is released from corn stalk and wheat straw while 7.78% and 20.98% S is released,respectively. The total amount of Na,Mg,K,Ca and Fe is hardly changed. A small amount of water-soluble K is transformed into ion-exchange forms,and part of water-soluble Mg and Ca are transformed into HCl-soluble forms. Under the same atmosphere,the mass increment after corrosion tests of torrefied biomass ash is slightly higher than that of the raw biomass due to the slightly increased AAEM (alkaline and alkaline earth metal) contents ash after torrefaction. Due to the presence of SO2,the sulfate reaction is caused,and the degree of corrosion is reduced,thus the mass increment after corrosion tests of co-combustion ash is obviously lower than that of individual combustion ash. After torrefaction,the elemental composition of bulk ash from both individual combustion and co-combustion has little change,so its influence on corrosion degree is limited. However,the increase of Cl in the corrosive atmosphere can significantly promote the corrosion behavior. Benefiting that torrefaction can remove part of Cl in the biomass,torrefaction is potential to reduce the corrosion tendency during combustion.