Optical power flatness is the difference between the optical power of each wavelength and the average optical power of all wavelengths on an OA.Use the multi-channel spectrum analyzer unit (MCA) to scan the optical power of all single wavelengths on an optical multiplex section (OMS), calculate the average optical power of all wavelengths that pass through the OA, and then calculate the difference between the single-wavelength optical power and the average optical power. Take an absolute value for each difference, among which the maximum value is the optical power flatness.