Abstract: In order to improve the its quality, Sargassum fusiforme was solid-state fermented by Aspergillus oryzae in this study. Based on the results of single factor experiment, the fermentation conditions were optimized by orthogonal experiment using total phenolic content as the index. Furthermore, the changes in the volatile compounds of S. fusiforme before and after fermentation were analyzed using solid-phase microextraction - gas chromatography - mass spectrometry technology (SPME-GC-MS). Results showed that the optimal fermentation conditions were: temperature of 27 ℃, media moisture content of 80%, initial pH value of 8.0, and fermentation time of 4 days. The total phenolic content of S. fusiforme was effectively enhanced and reached 4.24±0.213 mgGAE/g under the optimal fermentation conditions. 115 volatile compounds were detected in S. fusiforme raw matrix, and the volatile compounds were reduced to 57 after 4 days of fermentation, among them, 11 kinds of new esters (including methyl palmitate, methyl myristate, butyl propionate, and ethyl nonanoate, etc.) were formed, thereby effectively reducing the off-flavors of S. fusiforme. The results of this study showed that fermentation of A. oryzae is an effective method to increase the phenolic content and remove the off-flavors of S. fusiforme.