The three-dimensional reference interaction site model (3D-RISM) theory is a versatile developed molecular theory of solvation. The theory gives promise results that greater advantage to forecasting the hydration structure and thermodynamic quantities of protein than the conventional statistical-mechanical theories of liquids. In this works, we use 3D-RISM theory to examine protein hydration such as detecting water molecules in protein cavities, the pressure effects on protein conformation in terms of the partial molar volume (PMV) which also can explain thermodynamic behaviors of protein. Studying the pressure reversal of anesthesia which is almost impossible by the ordinary molecular simulation, give good results that agree with the experimental data. The 3D-RISM theory can be applied to many subjects in science like biochemistry, chemistry and biophysics like the study of conformational stability of protein against thermodynamic variable, the effects of cosolvent, like ions, alcohols, mixed solvents, etc.