The volatile compounds formation mechanism from the self-degradation of several amino acids was studied in subcritical water (SCW). The effect of pH on the self-degradation of several amino acids to generate volatile substances was discussed. The results showed that glycine (Gly)， L-alanine(Ala)， L-arginine (Arg) and L-aspartic acid (Asp) could not be degraded in SCW， which might be due to their simple structure and excellent thermal stability. In SCW system， L-serine (Ser) and L-threonine (Thr) could be decarboxylated to generate the intermediate structure of aminoacetaldehyde， then various pyrazine compounds were generated， which included 2，3，5-trimethyl pyrazine， 3，5-dimethyl-2-(3-methylbutyl) pyrazine， and 3，6-dimethyl-2-ethyl pyrazine. Benzaldehyde， phenylacetaldehyde， acetophenone， and 7-ethyl-1，3，5-cycloheptatriene were the major self-degradation products of L-phenylalanine (Phe). The key intermediate mercaptoacetaldehyde was formed from the self-degradation of L-cysteine (Cys)， and thiophenes， thiazoles， and polysulfides were formed by the reaction of mercaptoacetaldehyde with various aldehydes. According to the formation of volatile substances in each system， the possible volatile substances formation mechanism from various amino acids were proposed in SCW.