Abstract: The effect of agitation speed on agitation current field was studied in 5 L mechanically stirred bioreactor by computational fluid dynamics (CFD) method.Safflower (Carthamus tinctorius) cells were cultivated in stirred tank reactor under different agitation speeds.The resultant changes in the cells were evaluated on the basis of biomass,cell viability and change of fermentation liquor about pH,sugar concentration,DO,capacitance,conductivity and CER.Results showed that there was an adaptive process of cell cultured in the shear flow field.To a certain extent,cells were able to tolerate the shear force in mechanically stirred bioreactor with ε_ave,CFD≤0.8 W/kg.Under this shear flow field,the lag phase was shorter,and the speed of biomass accumulation and recovery of cell activity was faster.If ε_ave,CFD>0.8 W/kg,cells couldn't tolerate the shear force,because it was not easy for cells to recover cell activity,and even cells were lysised after suffering from damnification.