M+N theory can be used as a method to improve the prediction accuracy in spectral analysis. The measured component, M kinds of non-measurement component, and N kinds of outside interference are induced into the entire measuring system, with the impact of "M" factors and "N" factors on the measurement accuracy considered systematically and comprehensively. Our human experiment system testing blood oxygen saturation based on "M+N" theory has been established. Dynamic spectrum method was used to eliminate the effects of different persons and different measuring parts which belonged to the system error of "N" factors. And then the D-value estimation was used to eliminate the effects of motion pseudo signal which belonged to the random error of "M" factors. Sixty two groups of valid data were obtained. The prediction model of blood oxygen saturation was built based on partial least squares regression method. The correlation coefficient and relative error were 0.796 8 and ±0.026 6, while the result of oximeter was 0.595 7 and relative error was ±0.076 0, respectively. The results show that the prediction accuracy of the measurement method based on the "M+N" theory is much higher than that of the oximeter.