This paper proposes a nonlinear method of detecting the blood oxygen saturation (SpO2) in a wide range on the basis of spectrophotometry, solves the nonlinear problem in detecting SpO2 in a wide range, and improves the applicable range and detection precision. CAN bus communication and DSP fast digital signal processing are utilized in the design of a non-invasive pulse blood oxygen saturation (SpO2) monitor in a wide range, which has a measure error below 3% within a range of 35% approximately 100%, and is applicable for clinical monitoring and detection of cosmonauts' physiological signals. This oximeter's components and their functions are also introduced in detail in the paper.