A physiological detection system including an image sensor, a converting unit, a retrieving unit and a processing unit is provided. The image sensor includes a plurality of pixels respectively configured to output a PPG signal. The converting unit is configured to convert a plurality of PPG signals of a plurality of pixels regions to a plurality of frequency domain signals. The retrieving unit is configured to respectively retrieve a spectral energy of the frequency domain signals corresponding to each of the pixel regions. The processing unit is configured to construct a 3D energy distribution according to the spectral energies.