The method that noninvasively measures blood oxygen with near-infrared spectroscopy is widely used.The error reason that measures bow blood oxygen saturatio with conventional two-wavelength light,measure precision was improved with three-wavelength method.The calibration experimental results showed that the three-wavelength is accurate.Through comparison of system performance test,it showed that the syetem hod high accuracy and good real-time.The system has a wide application in low oxygen staturation monitoring.