Abstract: The wheat straw fibers after alkaline-AQ pulping was handled by oxygen directly without washing in present study. A L9(34) orthogonal design, including the factors of alkali charge, oxygen dosage, cooking temperature and holding time, was applied to evaluate their influences on black liquor viscosity and pulp Kappa number. The high quality pulp fibers with black viscosity 3.4 mPa·s and Kappa number 17.9 was obtained when the unwashed fibers were treated by 1% alkali charge (as NaOH) and 0.6 MPa oxygen pressure for 60 minutes at 85 ℃. In contrast to the pulp after first stage alkaline pulping, the black liquor viscosity and Kappa number decreased 33.3% and 11.8%, respectively.