This study presents the design, fabrication, characterization, and testing methodology of a reflective blazed grating operating in Littrow configuration. The grating, fabricated via mechanical ruling technology 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 blazed 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 measurement speed compared to conventional approaches, demonstrating potential for real-time dynamic characterization of grating devices.