Abstract: It could wash most of metal elements in corn stalk such as K, Ca, Mg and P by 0.01% dilute sulfuric acid. Equivalent metal chlorides were added to the washed corn stalk while pretreated with 0.1% dilute sulfuric acid, and hemicellulose degradation rate could reach 37%, enzymatic digestibility rate of the pretreated corn stalk could reach as much as 23%, while treated with 0.1% dilute sulfuric acid, the results were 17% and 12% respectively. Metal chloride produced a significant drop in pH value, but at the same pH value, when treated with pure sulfuric acid, hemicellulose degradation rate was 19% less than 37% when treated with 0.1% diluted sulfuric acid added with metal chloride. In addition, FeCl3 significantly increased the hemicellulose degradation rate. Metal chlorides, especially FeCl3 can promote hemicellulose decomposition, and the drop of pH value is not the vital cause.