Abstract: The ginsenoside isomers were analyzed and distinguished by using inlet ionization-high resolution mass spectrometry technology under positive and negative ion modes with optimum inlet temperatures. The results showed that under the full scanning mode of positive and negative ion modes with the optimum experimental temperature, different types of ions were formed according to the characteristics of different numbers of polymers formed by isomeric monomers of ginsenoside, and the identification of ginsenoside isomers was realized. For the identification of ginsenoside CK and Rh₂, there was no obvious difference in their MS spectra under positive ion mode. However, under negative ion mode with the inlet temperature of 200 ℃, ginsenoside CK tended to form polymers of M+Cl^－, Rh₂ tended to form polymers of M+COOH^－, and the number of polymers of CK was significantly higher than that of Rh₂. For the identification of ginsenoside Rb₂ and Rc, under positive ion mode with the inlet temperature of 200 ℃, ginsenoside Rb₂ and Rc could produce polymers of M+Na⁺, but the polymers peak intensity of Rb₂ was significantly higher than that of Rc. Under negative ion mode with the inlet temperature of 200 ℃, Rb₂ tended to form polymers of M+Cl^－, and Rc tended to form polymers of M+COOH^－. For the identification of ginsenoside Rg₁ and Rf, there was no obvious difference in their MS spectra under the positive ion mode. Under negative ion mode with the inlet temperature of 200 ℃, Rg₁ and Rf tended to form polymers of M+Cl^－ and M−H⁻, respectively. In this study, the three pairs of isomers in ginsenosides were basically identified by using the full MS scanning method and the control of the mass spectrometry inlet temperature. The experimental method is simple, fast, and has the characteristics of low consumption. This study confirms that the entrance ionization mass spectrometry technique can provide a theoretical reference for the rapid discrimination and identification of ginsenoside isomers.