To address the current reliance on theoretical calculations for evaluating the diffraction effects of aperture stops in irradiance measurement, an experimental method to detect diaphragm diffraction effects was developed. This aims to correct aperture stop diffraction and enhance total solar irradiance measurement accuracy. Utilizing dark-field imaging and Fraunhofer far-field diffraction theory, a detection method was designed and tested. By calibrating detector linearity, correcting background signals, and analyzing diffraction image data, a data correction process was established. This process determined the solar absolute radiometer diffraction effect value at the aperture stop's front structure and assessed the experimental uncertainty. The experiment found a diffraction effect value of 8.81×10^-4 with a total uncertainty of 6.49%. These findings provide a crucial technical foundation for accurately correcting diffraction effects in China's next-generation Fengyun meteorological satellites' solar radiation monitors, enabling precise total solar irradiance measurements.