Infrared chalcogenide optical glass is a material that is opaque to visible light. The method outlined in GB/T 7962 cannot be used to test its striae. Herein, test methods based on parallel light projection are presented to facilitate striae detection and characterization. The corresponding test equipment (chalcogenide glass samples) are developed and tested for striae and grayscale and modulation transfer function (MTF); further, the relationship between grayscale and MTF is investigated. Subsequently, the characterization method of striae severity with grayscale is proposed. The results show that the defects and distribution of the inner striae can be clearly detected after imaging in the near infrared band by parallel light projection. The mid-infrared MTF can qualitatively characterize the effect of striae on imaging quality. The striae can be used to quantitatively characterize the internal striae condition of the sample and reflect the effect on imaging quality. This paper provides a reference for the subsequent determination of the internal quality of infrared chalcogenide optical glass.