This study presents the design， fabrication， characterization， and testing methodology of a reflective blazed grating operating in the Littrow configuration. The grating， fabricated via mechanical ruling with a sawtooth profile， was characterized using a terahertz quantum cascade laser combined with self-mixing interferometry. Non-contact measurements yielded a grating constant of 84.89 μm and a blaze angle of 24.9°， with performance metrics including an angular resolution of 0.117 rad/THz and a peak diffraction efficiency of 71% within the terahertz band， consistent with theoretical predictions. By directly resolving grating parameters through laser feedback signals， this method significantly improved the measurement speed compared to conventional approaches， demonstrating the potential for real-time dynamic characterization of grating devices.