Abstract: A psychological stress index measuring system and its analysis method comprise a pulse generator, a transmission-based photo sensor, a signal converter & amplifier, a filter and a processing platform. At first, the transmission-based photo sensor fixed on a user depends on a light transmitting mechanism to detect analog SpO2 (oxyhemoglobin saturation by pulse oximetry) signals. Then, it will be processed and transformed to digital signals and further exported to the processing platform for extraction of PPGA & HBI. Finally, it will pass a median filter, normalization, and development of Psychological Stress Index which is based on the normalized PPGA & HBI as one convenient method to evaluate psychological health.