Raman spectroscopic studies on the process of dissolution and phase transition of gypsum in different fluids were taken. Gypsum took phase transition to be anhydrite in the range from 170 ℃ to 190 ℃ in pure water, and no more change happened with decreasing temperature to room temperature. Gypsum took phase transition to be anhydrite in the range from 170 ℃ to 190 ℃ too in Na2SO4 solution, but anhydrite can regain to be gypsum when temperature decreases to room temperature. The process of phase transition of gypsum in pure water is not reversible, but it happens in Na2SO4 solution. The study shows that fluid effects can influence the dissolution and phase transition mechanisms of minerals and cannot be ignored.