Abstract: In order to shorten pretreatment and dyeing process and improve the stability of enzymatic hydrolysis and dyeing in one bath,reactive dyeing of knitted cotton with the catalase-treated bleach effluents in one bath was investigated by comparing with traditional process.The effects of various concentration of H_2O_2 on the shade of the fabrics dyed with pure reactive dyes and mixed dyes were also observed.The results indicated that H_2O_2 had negative effect on the dyeing in the presence of Reactive Yellow 4-GL,Reactive Red B-3BF and Reactive Dark Blue B-2GLN.However,the effect on other dyes was insignificant.The enzymatic hydrolysis and dyeing effect in one bath can be improved by using soft water,decreasing the content of metal ions,adjusting electrolyte and dyes quantity.