Abstract: Foxtail millet is processed into porridge for human consumption. To determine the changes of physiological activators in the process, we analyzed the contents of amino acids, phenolic acids and flavonoids and antioxidant ability of extracts of instant foxtail millet porridge at different processing stages, including high pressure cooking, freeze drying and rehydrating. The results were as follows: the total amino acids and essential amino acids had no substantial change after processing. High pressure cooking significantly influenced the bound phenolic acids and free flavonoids content, which were reduced by 27.87% and 29.57%, respectively. Freeze-drying and rehydration had little effect on the content of phenolic acids and flavonoids. Content of vanillic acid increased significantly after processing, rose by 73.94% after rehydrating. After rehydration, the DPPH scavenging ability of free and bound phenolic acid extracts were reduced by 55.83% and 88.39%, respectively. After high pressure cooking, ferric iron reduction ability of free and bound phenolic acid extracts were reduced by 30.08% and 39.74%, respectively, declined significantly, freeze drying and rehydration had no significant effect on ferric iron reduction ability of phenolic acid extracts.