Based on the principle of photoacoustic effect,a highly sensitive photoacoustic sensor is made using carbon black as absorption sample,whose absorption coefficient is 1.And we use the photoacoustic sensor as a power monitor which is an ideal non choice detector for the electron detector.As a result,the dependence of the quantum efficient of the electron detector on the wavelength of the xenon light is removed.By means of the normalized photoacoustic spectrum technique,the relative spectrum responsibility of detector is truly measured.