Changes of the accuracy and performance of the fire-damaged machine tools were investigated in this paper. First, we measured the intact accuracy of the lathe bed of the fire-damaged machines, and found out the considerable change in its shape. Because we understood the cause of this change depends on the difference of the fire conditions, we made researches on the model lathe beds in the variation of the temperature, time and the various aftertreatment of the heated beds. The result of experiments revealed that the shape changes were no so conspicuous at the temperature up to 600°C, but were remarkable at the temperature ranging from 600°C to 800°C. The further temperature rise caused the rapid degradation of accuracy and the water jet upon the heated parts caused the marked deformation.