To study the fragmentation pathways of harmaline and harmine by etectrospray ionization mass spectrometry (ESI-MSn). Methods:Harmaline and harmine were analyzed by ESI-MSn in positive ion mode. The first and multi-stage mass spectrum diagrams were obtained. Results:To analyze mass spectrometry fragments of the harmaline and harmine， under the positive mode， RDA decomposition occurred mainly， and –CH3， -OH were lost. Conclusion:The results enriched the mass spectrum decomposition， and provided the basis for the chemical constituents research of β-carboline alkaloid.