Abstract: This work explores birefringence behavior for injection molded amorphous polymers. Photo-elasticity method was used to measure the gapwise-averaged birefringence of PS plaque parts molded under different process conditions. The effects of melt temperature and packing pressure on the birefrin-fence distribution were investigated.It was found that residual birefringence decreased from the area near the cavity entrance to the end of the part along the melt flow direction，decreased with incrcasing temperature and decrcasing packing pressure. Especially, higher packing pressure exhibited significant effect on birefringence distribution of the area near the date. Flow-induced residual stress and molecular
orientation distribution of injection molded PS part were evaluated from the birefringence distribution measured by photo-elasticity method.

Key words: injection molding, birefringence, photoclasticity, flow-induced residual stress, molecular oncntation