The invention discloses a gas-phase molecular absorption spectrometer, comprising a sample introduction device, a gas-liquid separation device, a drying device and a detection device, characterized in that the gas-liquid separation device comprises a sample inlet 1, a reaction chamber 2, a gas outlet 3, A connector outlet 4, a waste liquid outlet 5 and an air pressure balance port 6, the sample inlet 1 communicates with the reaction chamber 2, and the reaction chamber 2 communicates with the waste liquid outlet 5 through the connector outlet 4 It communicates with the air pressure balance port 6 . By adopting the gas-phase molecular absorption spectrometer provided by the invention, the operation is simplified, the objectivity of the analysis result is enhanced, the analysis sensitivity and precision are better, automatic online heating is realized, and the application range is wider.