To investigate the differences in taste quality among oysters from various geographical origins and with different fattening durations, this study analyzed and compared the contents of taste compounds and taste quality indicators (taste activity value (TAV); equivalent umami concentration (EUC)) in diploid and triploid oysters from eight coastal regions in Guangdong and triploid oysters fattened in the waters of the Chuan islands, Taishan for up to 5 months. Partial least squares-discriminant analysis (PLS-DA) was employed to identify key differential compounds influencing oyster taste. On this basis, factor analysis was used for comprehensive evaluation of the taste quality of oysters in order to establish a comprehensive evaluation method. Significant differences in taste were observed among oysters from different geographical origins. The main differential compounds contributing to umami and sweet tastes were glutamate (Glu), alanine (Ala), glycine (Gly), threonine (Thr), arginine (Arg), and succinic acid (SA). Four common factors were extracted through factor analysis, cumulatively explaining 91.643% of the variance. Oysters from Zhanjiang (ZJ), Taishan (HLW and SCD), and Chaozhou (RPT) ranked high in terms of overall scores for taste quality. Triploid oysters SCD and RPT showed superior performance in the umami/sweet amino acid and organic acid factors, while diploid oysters ZJ and HLW exhibited advantages in the nucleotide synergistic factor. Differences in taste quality were also noted among oysters with different fattening durations, with the main differential taste compounds being Gly, Glu, Ala, and proline (Pro), along with inosinic acid (IMP). Three common factors were extracted, cumulatively explaining 94.402% of the variance. The overall score for taste quality of oysters reached its highest value after 3 months of fattening and then declined with increasing fattening time to 4 and 5 months. These findings provide a scientific reference for the breeding, processing, and resource utilization of oysters.