Niulanshan baijiu (NLS), as a famous brand and national cultural heritage in China, is a representative of light-flavor baijiu (LFB) and is popular among consumers for its purity, pleasantly fruity, mild taste, and refreshing aftertaste [8]. The baijiu flavor formation is mainly dependent on its unique fermentation process, distinct starter, carefully selected raw materials, and special fermentation workshops. NLS adopts Erguotou-producing craft and is brewed by using high-quality wheat, barley, and peas to make low-temperature Daqu. Sorghum from Northeast China is used as the raw material, and an earthern jar (Digang) is used as the classic fermentation container [9]. Much progress has been achieved in the fermentation process and flavor generation of NLS in recent years. For example, four unclassified bacteria were unique, and the ratio of fungi to bacteria was the highest in Niulanshan Daqu when compared with other aroma-type Daqu, including Wuling Daqu (jiang-flavor), Baisha Daqu (mixed-flavor) and Deshan Daqu (strong-flavor) [10]. In addition, the composition, drivers, and functions of the active microorganisms in the fermented grains were revealed by metatranscriptomics systematically, which was different from reports about the dominant microorganisms during fermentation [11]. Moreover, the phylogeny and population structure of the amylolytic yeast _Saccharomycesfibuligera_ from Niulanshan Distillery were analyzed, and these strains were distributed in the same lineage from the fermented grains and low-temperature Daqu [12]. Meanwhile, a total of fifty nine odorants were found in NLS samples at different storage years, and five of them were first identified as aroma-active compounds in LFB [9]. Among all the mentioned fermentation parameters, fermented grains are the main carrier of microbial fermentation and the direct contributors to baijiu flavor [13]. Therefore, fermented grains, where microbial communities play a vital role, and flavors are formed, have always been the focus of baijiu fermentation research. Based on metagenomics and metabolomics analysis of the fermented grains from Fenjiu Distillery Co., Ltd., the correlation between microorganisms and their function was established [8]. Additionally, the effects of fermentation periods on the flavor components of light-flavor Xiaoqu baijiu were studied by HS-SPME-GC-MS. The esters and alcohols, including ethyl acetate, diethyl succinate, phenylethyl alcohol, ethyl hydrogen succite, and n-propanol, accumulated to the highest abundance after 98 days of fermentation. In contrast to the normal fermented grains, the content of n-propanol was increased significantly in the ultra-long fermentation samples [14]. Our previous study based on metatranscriptomics clarified the active microbial composition, drivers, and their functions in NLS fermentation. However, the dynamic change in the metabolites and the active functional microbiota contributed to the volatile flavors in the fermented grains are poorly understood, generating a mystery of NLS flavor formation. In this study, integrated metatranscriptomics and untargeted metabolomics were employed to elucidate the dynamic changes in metabolites and the potential correlation between the active microbiota and the volatile flavors based on the O2 PLS-DA model. Furthermore, the active functional microbiota involved in the production of the volatile flavors was identified. Herein, we provided an overview of the comprehensive metabolite compositional variety and the contributed active functional microbiota in the fermented grains in the hope of facilitating a better understanding of flavor formation and providing the basis to improve the quality of NLS.