Screened and unscreened oxygen-alkali pulps of wheat straw were bleached via QPo and OQPo sequences,and the bleaching effects were compared between screened and unscreened pulp.Furthermore,both the characteristics of the fibers in bleached pulp and the pollution load of the effluent were analyzed.The results show that,as compared with QPo bleaching sequence,OQPo bleaching sequence may result in higher brightness,heavy viscosity loss and low yield for both the screened and the unscreened pulps;that,as compared with the screened pulp,the unscreened pulp is of higher brightness-increasing rate（up to 4.9 percentage points） and total pulp yield（up to 10.6 percentage points）;that the fibers in the screened pulp is about 0.78 mm in weight-average length,which is similar to those in the unscreened pulp,while the fiber coarseness of screened pulp is much higher;and that OQPo bleaching is more environmentally friendly than the traditional CEH bleaching because it completely eliminates absorbable organic halogens and greatly reduces CODCr and BOD5 discharge.