A noninvasive monitoring method for brain edema based on near infrared photoelectric detection technology is proposed. The measurement principles and system composition of the monitoring instrument are studied. The light source of the instrument is 760 nm and 850 nm dual-wavelength LED, which is driven by constant current source module. The light signal, scattered from the tissue, is detected by OPT101. Then the signal is processed by phase-locked amplifier and filter circuit. The filtered data are sampled by data acquisition card and processed in the LabVIEW environment in computer. The proposed system can monitor the changes in the brain of hemoglobin on real time. The system is used to monitor the changes of light intensity and blood oxygen content of the model of brain edema in mouse. The relationship between the changes of light intensity and oxygen parameters and brain edema is studied. The experimental results show that the near infrared photoelectric detection technology can be used as the noninvasive monitoring method for brain edema.