Abstract: This paper investigated diurnal variation and daily change of the oxygen content in the air over Lhasa city, and analyzed the cause with meteorological factors.Resultsshow:1) the content has a obvious peak and valley value.2) the oxygen content has negative relation with relative humidity and it has no close relation with temperature, air pressure.3) Comparing with the content over sea-level area, the oxygen content over Lhasa city is smaller than the mentioned area.4) There is no direct relationship between oxygen content with oxygen quality per cubic meter of air, it can not be used to measure the Absolute content of oxygen in the air.