In the process of magnesium hydroxide dissolution by carbonated water with CO2 pressure between 1 and 5 MPa, no solid product was found covering the solid Mg(OH)(2). A reaction mechanism was proposed, where the hydration of Mg2+ was emphasized. The kinetic model for the dissolution was derived, which fitted the experiment data well and could be applicable to other dissolution reactions without solid product but soluble one highly binding with the solvent. A concept of "progressive liquid film" was introduced to this reaction system for the first time. The pressurized magnesium hydroxide dissolution was found to be rate-controlled by the diffusion in the progressive liquid film around the solid Mg(OH)(2). Based on the Arrhenius expression, the apparent activation energy at stirring speed of 200, 300 and 400 rpm was obtained as 17.1, 25.1 and 25.4 kJ/mol, which also indicated that the dissolution inclined to be diffusion rate controlled. Moreover, the apparent diffusion coefficients of H+ in the liquid film were calculated and an empirical expression was obtained for the first time as well.