Astaxanthin (AST), the natural pigment in Litopenaeus vannamei, is susceptible to oxidation and isomerization, leading to the fading of the orange-red color in ready-to-eat (RTE) shrimps. This study specifically investigated the changes mechanism in AST content, including geometric and stereoisomers, as well as oxidation degradation, throughout the storage process of RTE shrimps. The results showed that the total amount of AST decreased by 46.76 % after 45 days of storage at 40 °C. The levels of geometric isomers (all-E, 9-Z, 13-Z) and stereoisomers (3S,3'S, 3S,3'R, 3R,3'R) gradually decreased over time. Notably, 9-Z and 3S,3'S isomers, known for their strong antioxidant activity, were reduced by 83.57 % and 61.64 % respectively. Additionally, AST underwent oxidative degradation, forming short-chain compounds (astaxanthinal or astaxanthinone), with the main products being Apo-14'-astaxanthinal and Apo-7-astaxanthinone DHA ester. These findings provide a theoretical foundation for further research on the degradation mechanism of AST, and offer valuable insights into the color protection of RTE shrimps.