The invention discloses a blood 
oxygen saturation measuring method and instrument and belongs to the technical field of measurement. The method includes utilizing light sources to emit 
red light and 
infrared, utilizing photoelectric receivers to acquire the maximum value and the minimum value of 
red light signals and 
infrared signals to obtain the ratio of the difference value of the maximum value and the minimum value of the 
red light signals and the difference value of the maximum value and the minimum value of the 
infrared signals, arranging the light sources and the photoelectric receivers in the way that at least two different distances are formed between the light sources and the receivers, repeating the steps to obtain more than two ratios, determining the ratio with the largest absolute value in the more than two ratios to calculate a blood 
oxygen saturation measuring value, wherein one 
light source and more than two photoelectric receivers with different distances between the 
light source and the receivers or one photoelectric 
receiver or more than two light sources with different distances between the 
receiver and the light sources are adopted to achieve the arrangement that at least two different distances are formed between the light sources and the receivers. By means of the blood 
oxygen saturation measuring method and instrument, the accurate blood 
oxygen saturation measuring value can be obtained, the blood 
oxygen saturation measuring accuracy is improved, and the use is simple.