To provide a method and an apparatus for continuously measuring a partial pressure ratio of mixed gas in real-time without destructing the mixed gas.

The method for measuring the partial pressure ratio of the mixed gas nondestructively in real-time based on a measured resonance frequency of the mixed gas in a container includes steps of inserting mixed gas of which temperature and pressure are controlled or measured, oscillating a sound in the mixed gas in a resonance vibrational state, measuring a resonance frequency of the sound, obtaining propagation velocity of the sound in the mixed gas based on the temperature and the pressure of the mixed gas, and determining a partial pressure ratio of the mixed gas based on the propagation velocity.