The invention relates to a sample inlet gas stable-pressure and quantitative rarefaction component applied to a gas detector for a mass spectrum and the like, which is composed of a three-way connector (T1), a vacuum rarefied chamber (S1) and a vacuum adjusting system along a flow direction of sample inlet gas, wherein the vacuum rarefied chamber (S1) is connected with the sample inlet gas through the three-way connector (T1); the other connector of the three-way connector (T1) is connected with the other detector (J2) or is evacuated; a branch at one side of the vacuum rarefied chamber (S1) is connected with the vacuum adjusting system; the vacuum degree of the vacuum rarefied chamber (S1) is adjusted through the vacuum adjusting system; and the sample inlet gas enters the detector (J1) through the vacuum rarefied chamber (S1). By using the sample inlet gas stable-pressure and quantitative rarefaction component, the stability of gas pressure and flow rate in a detection process can be improved, the sample gas amount entering the detector is reduced and the service life of an analyzer is prolonged; the combination of various detectors can be realized; and therefore, the sample inlet gas stable-pressure and quantitative rarefaction component can be commonly used for the condition that a detection system is not stable due to high concentration of the gas.