Abstract: In this study, along with the addition of 4% and 6% sugar and salt, effect of lactic acid bacteria fermentation, yeast fermentation and both of them co-fermentation on Laminaria japonica (L.japonica) were investigated, thereafter the flavor changes of which were determined by gas chromatograph-ion mobility spectrometer (GC-IMS). The volatile organic compounds (VOCs) of L.japonica were identified and compared before and after fermentation, the fingerprint spectra were established, and the differences between different fermentation conditions were analyzed by principal component analysis (PCA). According to the results of the fingerprints, there were significant differences between the VOCs in the fermented samples under different conditions. Totally 33 VOCs were identified in the fermented samples, including aldehydes, alcohols, ketones, carboxylic acids, esters, ethers and aromatic compounds, of which aldehydes, alcohols, and ketones were main substances. The contents of aldehydes was the highest before fermentation, while after fermentation by yeast, the content of certain aldehyde of low molecular weight such as hexanal, heptanal, and pentanal were significantly reduced, which resulted in the reducing the fishy smell of L.japonica. PCA results showed that the contribution rate of the first two main components was 86.58%, which could represent the characteristics of the samples basically. In addition, samples under different fermentation conditions were well distinguished. According to this study, fermentation was an efficient way to reduce the fishery smell and thus improve the flavor of L.japonica. GC-IMS technology could be effectively applied to distinguish different fermented samples, and had potential application value for the construction of fingerprints and databases of VOCs of L. japonica.