In order to solve the technical problems of complex optical path and large error of the traditional spectroscopic spectroscopy ratio and reflective transmittance measuring method, the invention provides a spectroscope measuring method and device capable of accurately controlling the incident angle. The error of the measured optical path is reduced using a small aperture, a pentaprism and a secondplane mirror self-alignment method based on the characteristic that the spectroscope reflects part of light; a 45-degree incident angle reference is calibrated using a vertical incidence method of anauto-collimation light pipe; precise control on the small angle change of the incident angle of the spectroscope is realized using the angle detection function of the auto-collimation light pipe; andwhen the precision of the auto-collimation light pipe is 1', the incident angle control precision can reach 0.5' magnitude.