Residual stress distribution and surface molding state of polymeric materials are presented for thin-walled injection molding. The residual stress is computed by computational numerical analysis, observed with a stress viewer and birefringence. The residual stress on the surface of the polymeric part can indicate the surface quality as well as flow paths. The residual stress distribution of the polymeric part is related with the part’s thickness, the gate layout, and the polymer type. Molecular orientation, affected by flow paths, is simulated and validated by observing the birefringence of the polymeric specimens. The residual stress and molecular orientation are closely related to the surface molding states.