In the following paper, density functional method and Universal QUAsi-chemical (UNIQUA) activity index model were applied to calculate the concentration of Alanine I supercritical water. B3LYB method and 6-311G+ (2D, 2P) basic function were used to optimize the molecular structure of Alanine, water and Alanine water complex. Then, reaction parameters of UNIQUAC model were calculated, using formation energy values. PCM method and zeropoint energy were utilized to include solvent effect and BSSE effect respectively. The resulted errors indicate that the method in a fairly good agreement with the experimental data. IncludingSSE in the interaction parameter calculations reduces the total error significantly. According to our calculations theAlanine- water complex showed a negative deviation from Raoul’s law.