Abstract: To explore the differences in volatile substances and critical nutrients between sea buckthorn leaves and freeze-dried powder obtained by vacuum freeze-drying. The volatile components, amino acids, and soluble sugars of sea buckthorn leaves and their freeze-dried powder were systematically characterized by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry. Results showed that 64 volatile compounds were detected in sea-buckthorn leaves, and 60 volatile compounds were identified in freeze-dried powder, including 26 newly generated substances after processing. The odor active values (OAV) analysis and aroma profile showed that sea buckthorn leaves had higher green, fruity, and sweet intensity. In contrast, freeze-dried powder showed higher floral, green, and fat aroma properties. In addition, there were 13 amino acids and three sugars with high content in sea buckthorn leaves and freeze-dried powder. In particular, leucine and alanine significantly correlate with most volatile compounds, such as 2-methyl-butanal and furfural. The results can provide a reference for subsequent research on the flavor characteristics of sea buckthorn leaf instant powder and its development and promotion.