Virtual internal hyperspectrum of body surface which can express and properly mix the information of skin’s composition and structure was expected to apply in the human disease quick-diagnosis, but the weak detected signal was easily impacted by ambient light and dark current from the instrument, so square wave modulated by chopper disk was proposed to resolve this issue. First, we built the experiment platform, and selected both laser and bromine tungsten lamp as the light source, then compared the virtual hyperspectrum of non-modulated and modulated light on human arm in the environment with artificial interference, and demodulated the modulated signal by FFT method. The experiment result showed that modulation method could effectively eliminate the impact brought by environmental light and dark current and improve the signal to noise ratio (SNR)， suggesting a new approach to detect human’s weak optical signals.