Abstract： A cerebral oximeter based on 3-wavelength spatially resolved spectroscopy and the modified Lambert-Beer law is proposed.A platform for monitoring the regional cerebral oxygen saturation(rSO2)is established,and the system reliability is verified through spectral stability and background noise test.Eighteen volunteers are recruited to participate in the controlled hypoxia test for exploring the trend of rSO2 with the sequence of stepped hypoxia platform and discussing the relationship between rSO2 and arterial blood oxygen saturation.The results show that the established system can effectively monitor rSO2 and meet the measurement requirements.During the controlled hypoxia sequence,as the fraction of inspired oxygen decreases,rSO2 shows a downward trend,and the individual rSO2 has a high correlation with arterial blood oxygen saturation.