Fresh leaves from ‘Subei Zhong’ were used to make Fuzhuan brick tea and white brick tea to analyze the mechanism of forming the characteristic “fungus aroma” in Fuzhuan brick tea.Artificial inoculation with Eurotium cristatum was conducted under two conditions including monofungus fermentation by artificial inoculation （inoculated only with E. cristatum） and traditional fermentation.Metabolomics was used to analyze the dynamic changes in key aroma compounds associated with the characteristic “fungus aroma”.The gene expression profile of E. cristatum during the process of monofungus fermentation was further studied by combining with transcriptomics.The results of analysis with metabolomics showed that the level of （E，E）-2， 4-heptadienal （E，E）-2，4-nonadienal，（E，Z）-2，6-nonadienal and other key alkenal compounds that contribute to the formation of fungal aroma in Fuzhuan brick tea was significantly higher than that in white brick tea.The content of alkenal compounds significantly increased at the later stage of traditional fermentation， while the content of unsaturated fatty acids， the precursor substances of alkenal compounds， increased at the later stage of monofungus fermentation.The reason may be that the metabolic pathway for producing alkenal compounds is inhibited during the process of fermentation.The results of sequencing transcriptome showed that more than 96% of clean reads were identified in the genome of E. cristatum， with an average of 94% of the genes having unique locations in the genome.The results of annotation analysis showed that fatty acid-related genes serving as carbon sources for E. cristatum were enriched in the linoleic acid and alpha-linolenic acid metabolic pathways， and the linoleic acid metabolic pathway was annotated into two lipoxygenases.The lipoxygenase corresponding to the alpha-linolenic acid metabolic pathway was not annotated.Fatty acid consumption was reduced， leading to their accumulation during the process of fermentation with E. cristatum.Moreover， the alpha-linolenic acid metabolic pathway in E. cristatum was not annotated with lipoxygenase， indicating that this fungus cannot produce di-unsaturated aldehydes via the lipoxygenase oxidation pathway.This explain why the level of （E，E）-2，4-heptadienal and （E，E）-2，4-nonadienal in the tea of monofungus fermentation was significantly lower than that in traditionally fermented tea.Therefore， monofungus fermentation alone fails to develop the characteristic “fungus aroma”.There may be signal transmission and substance exchange among other microorganisms in the complex environment of traditional fermentation， which work together to ferment and convert unsaturated fatty acids into volatile alkenal compounds by E. cristatum.It is indicated that the formation of characteristic “fungus aroma” is achieved through the synergistic fermentation of the basic aroma of raw dark tea and the microbial community mainly composed of E. cristatum.