Serious corrosion of reactor metal walls by aqueous dilute acid solution is one of the essential drawbacks of dilute acid pretreatment (DAP) in the biorefining of lignocellulose biomass. In this study, the corrosion of pretreatment reactor metal walls was significantly reduced by the dry dilute acid pretreatment (DDAP) of corn stover, a modified DAP, in which the aqueous dilute acid solution is completely absorbed by high solids corn stover feedstock. The iron ion release from the stainless-steel walls of the reactor was measured, and the corrosion degree was quantitatively characterized. The reactor corrosion was reduced by approximately 85% when the solid/liquid ratio increased from the conventional value,of 1:10 to the high value of 1:0.5 at the same sulfuric acid concentration in the DDAP. The results provided the simple and practical solution to the key technical barrier of DAP and paved the way for large-scale application.