In order to calculate the stress distribution of the polymer melts in flow field,the conventional equipment of birefringence measurement is improved by reasonably rearrange the optical components in this paper,and a novel method to calculate the stress distribution of polymer melt in flow fields by measuring the flow-induced birefringence is proposed.The image obtained from this method contains both the information of the birefringence and the orientation angle,the orientation angle of the image is 45°where the light intensity gets maximum or minimum,so the shear stress alone the isoclinic line of an angle of 45°can be calculated,the deficiency of the conventional equipment that only used to measure the tensile stress along the axis of symmetry is overcome.In the last,the flow field of LDPE1810D in a self-made visualization die in extrusion condition was measured by using this equipment;the distribution of stress,along the isoclinic lines of an angle of 45°,was calculated.It is proved that this method is capable of the measurement of the birefringence of the flow fields,thus the stress distribution.