The invention discloses an etalon effect suppression method and device for detecting residual oxygen in a glass vial. The method comprises the steps that the main transmitted light intensity of laserwhich penetrates the glass vial and the transmitted light intensity after twice reflection are acquired and converted into a first current signal; the transmitted light intensity after the reflectionof the laser through the glass vial and the transmitted light intensity after three times of reflection are acquired and converted into a second current signal; according to the first current signal and the second current signal, output current is acquired; the second harmonic current signal of the output current is extracted; and the oxygen concentration is acquired according to the second harmonic current signal. The technical problem of low detection accuracy of residual oxygen due to optical noise caused by the interference of a beam generated by the wall of the glass vial to the second harmonic in the prior art is solved. By eliminating noise in the second harmonic from the signal detection part, the etalon effect can be suppressed from the source. The oxygen concentration detection accuracy and system stability are greatly improved.