Expansibility and corrosivity of anhydrite and gypsum are the main disease-causing factors in gypsum rock tunnel engineering. Investigation of the mineral compositions, hydration characteristics, and contents of anhydrite and gypsum is the basis for evaluating the engineering hazard of gypsum rock. However, there is a lack of quick and simple method to determine the content of gypsum. By measuring the wave velocity and hydration depth in the hydration process of anhydrite rocks, the hydration characteristics of gypsum rocks are analyzed. Through the thermogravimetric analysis of anhydrite, gypsum, calcite and dolomite mixtures with different proportions, a thermogravimetric analysis method for rapid determination of mineral content of gypsum rocks is proposed. The results show that (1) thermal analysis, X-ray diffraction and infrared spectroscopy are recommended for the identification of mineral components of gypsum rocks. (2) Hydration of anhydrite rocks is slow, and it takes about 2 years for anhydrite rocks of the standard size specimen to be fully hydrated into gypsum rocks. (3) The hydration rate of intact anhydrite in the pure water environment is about 3 mm/a. If the groundwater environment is rich in ${\rm{SO}}_4^{2-}$, the hydration rate of anhydrite will increase. The established method for determining the mineral content of gypsum rocks can quickly determine the contents of anhydrite and gypsum. The study results provide a reference for analyzing the engineering hazards of gypsum rocks.