ObjectiveBased on the quality evaluation experience of "it is better to have a fragrant and strong aroma" summarized by materia medica of past dynasties， the chemical components of Sojae Semen Nigrum（SSN） and Sojae Semen Praeparatum（SSP） were systematically compared and analyzed， and the main fermentation products in different fermentation time were quantitatively analyzed， so as to clarify the transformation law of internal components in the processing process and provide scientific basis for the modern quality control of SSP. MethodUltra performance liquid chromatography-quadrupole tandem time-of-flight mass spectrometry（UPLC-Q-TOF-MS） was used for the structural identification of the chemical constituents of SSN and SSP， and with the aid of Progenesis QI v2.3 software， the negative ion mode was employed for principal component analysis（PCA） pattern recognition， and the data were analyzed with the aid of orthogonal partial least squares-discriminant analysis（OPLS-DA） for two-dimensional data to obtain S-plot， and components with |P|>0.1 were selected as the differential constituents. The contents of isoflavonoids in SSP during fermentation was determined by UPLC， and the samples were taken every 8 h in the pre-fermentation period and every 2 d in the post-fermentation period， and the dynamic changes of isoflavonoid contents in different fermentation stages were analyzed. The contents of amino acids and nucleosides in SSP and SSN from different fermentation stages were quantitatively analyzed by phenyl isothiocyanate（PITC） pre-column derivatization and high performance liquid chromatography（HPLC） gradient elution， and the contribution of flavor substances to the "delicious" taste of SSP was discussed by taste intensity value（TAV）. ResultA total of 19 kinds of differential components were screened out， mainly soybean saponins and isoflavones， and their contents decreased significantly or even disappeared after fermentation. In the pre-fermentation process of SSP， glycoside bond hydrolysis mainly occurred， and isoflavone glycosides in SSN were degraded and converted into the corresponding aglycones， the content of flavor substances such as amino acids increased gradually. In the post-fermentation process， protein degradation mainly occurred， after 8 d of post-fermentation， the content of isoflavones was basically stable， while the total content of amino acids increased by 8-40 times on average. Different amino acids form the special flavor of SSP， such as the TAV of glutamate is always ahead of other flavor substances， and sweet substances such as alanine and valine have made relatively great contributions to SSP. ConclusionBased on the law of constituent transformation， combined with the traditional evaluation index of "fragrant and strong"， it is difficult to control the fermentation degree of SSP by the existing standards in the 2020 edition of Chinese Pharmacopoeia. It is suggested that description of the characteristics of SSP be refined and changed to "fragrant， delicious and slightly sweet"， and at the same time， the post-fermentation index compounds such as glutamic acid， alanine and valine should be added as the quality control indicators of SSP， so as to standardize the production process and improve the quality of SSP.