We studied theoretically the reaction of glyceraldehyde hydrolysis, at the B3LYP / AUG-cc-pVDZ level. At first, we applied elementary reactions which defined as dehydration, keto-enol isomerization, and retro-aldol reaction to reaction pathways on glyceraldehyde conversion. The stationary point geometries were fully optimized and characterized as minima or first order saddle points by calculations of vibration frequencies. To estimate zero-point and thermodynamic corrections, we performed the frequency calculations at a temperature 773 K and a pressure 250 atm. Six-membered ring-like transition structure and presence of water promote the dehydration. But the presence of water hindered the isomerization mechanism. Furthermore, the unimolecular isomerization had significantly lowered the activation energy. The retro-aldol reaction could form the six-membered ring-like transition structure, which reduced the activation energy as well as the dehydration. Finally, glyceraldehyde can be converted into acrolein by the isomerization to propen-1, 2, 3-triol, followed by the dehydration. The subsequent keto-enol isomerization of acrolein produces pyruvaldehyde, which is overall rate-determining step. Furthermore, the retro-aldol reaction of glyceraldehyde can produce formaldehyde and 1, 2-ethenediol. The latter compound converted into glycolaldehyde by means of the isomerization. However, this pathway from glyceraldehyde is not main route of the glyceraldehyde conversion, because the activation energy on this route is less small than that on the formation of pyruvaldehyde. In the future study, reaction analysis with solvation model must be accomplished via QM/MM approach to elucidate solvent effect in supercritical water.