The expanding properties of limestone from 200°C to 700°C were investigated under high temperature and bidirectional restraints with the device used to heating rock designed by ourselves. The experimental results show that the two directional expanding stress of limestone increased with temperature increasing during raising temperature before 600°C, and decreased after 600°C. The expanding stress perpendicular to bedding plane was bigger than that parallel to bedding plane. The curves of expanding stress and temperature ascend steadily during constant temperature before 600°C, but the slopes were much less than those during raising temperature. The expanding stress tended to steady value at last with the time of constant temperature prolonging. The expanding stress when constant temperature ended was smaller than those before constant temperature at 700°C. It showed that the limestone had expanded to the limit value after a certain temperature. The expanding stress reduced possibly after a certain temperature because the rock sample was restricted and some fissures closed and the number of cracks reduced after over-high temperature, but the detailed cause needs more researches to testify it.