Spalling must be considered when designing high-strength concrete to cope with fire. This study investigates the temperature rise of steel bar in high-strength concrete coated with fireproof mortar using gypsum exposed to fire. It was found that fireproof mortar using gypsum is more effective in constraining the temperature rise of steel bar in the high strength concrete than fireproof mortar using cement, and that the thinner the cover depth of the fireproof mortar, the more significant the influence of the gypsum. In addition, while there was no difference between ${alpha}$-hemihydrate mortar and ${eta}$-hemihydrate mortar on the temperature rise of steel bar, the compressive strength of ${alpha}$-hemihydrate mortar is higher than that of ${eta}$-hemihydrate mortar.