Hemicellulose from corn stalk was extracted by hot water-dilute alkali. An investigation was made to the influence of hemicellulose pre-extraction on the cook- ing and bleaching properties of corn stalk and the differences of the ultrastructure of the fibers after cooking were compared. Results show that compared with pulp from unpretreated material, the brightness of both unbleached and bleached pulp from pretreated pulp rises by about 5%~10%ISO, its Kappa number decreases by 43.9%, the tear index increases by 72.3% while the breaking length and burst strength decrease by 6.5% and 7.6% respectively. AFM analysis on the surface of pulp fiber indicates that the substances with hemicellulose and lignin deposited on the pulp surface from pre- treated material disappear and much cellulose microfi lament exposes which caused the decrease in Kappa number and the increase in tear index.