A gas analyzer includes a reference gas chamber and a measurement gas chamber in a single cavity, and a micro-flow infrared gas detection device. A water adjustment device is disposed in the micro-flow infrared gas detection device. By identifying the overlapping phenomenon of the absorption spectrums of the gaseous water and the gas to be measured and by taking advantage of the difference between the infrared absorption spectrums of the gaseous water and the gas to be measured, the water adjustment valve is adjusted to change the velocity variation due to the expansion of the gas in front and rear gas chambers and the water adjustment buffer gas chamber of the micro-flow infrared gas detection device, such that the detected infrared spectrum is located within the absorption spectrum of the gas to be measured while away from the absorption spectrum of the gaseous water, thus addressing the water interference issue.