According to CCAR25.1443(c), passenger’s tracheal oxygen partial pressure shall be above 100 mmHg and 83.8 mmHg at some specific altitudes. The tracheal oxygen partial pressure can be converted to the equivalent height of breathing air by mathematical formulas according to related environment and physiological studies. The hypoxia level of passenger can be expressed by blood oxygen saturation when breathing air at the equivalent height. In order to verify that the oxygen supply level can meet the requirements of CCAR25, SaO2 test is required. The SaO2 value corresponding to the CCAR25 is the baseline SaO2. It’s the precondition of oxygen supply performance verification test for oxygen dispensing unit. This paper firstly uses mathematical formulas to calculate and determine the cabin altitude corresponding to the baseline SaO2 when breathing air; then selects test subjects according to the principle that shall be able to cover the greatest extent population; finally has a human body test of SaO2 of every subjects at the determined cabin altitude. The equivalent heights of CCAR25 requirement are 10 000 ft and 14 000 ft. The mean baseline SaO2 is 90.9% at 10 000 ft the number is 84.7% at 14 000 ft. At the two heights, human body will have a slight hypoxia response but no significant effect on efficacy.