Abstract: The effect of zircon additive on the microstructure of calcia- rich magnesia-calcia materials, the bonding way and properties of ZrO₂ and SiO₂ with MgO and CaO have been studied.The results are as follows:The crushing strength of specimens decreases after adding zircon; The effects of the different additions of zircon on the loss rate of MOR (modulus of rupture)of the material are quite different when the thermal shock temperature is 1100℃. The loss rate of MOR of specimens is the lowest when the addition of zircon is 4%; The crystal size of MgO in matrix to which zircon is added, is bigger than that of the specimen without zircon addition. With the formation of CaZrO₃, the specimen has the expansion in volume. SEM observations found that there were radial microcracks around CZ(CaZrO₃) grains. It is the existence of these kinds of microcracks that increase the mechanism of consuming energy which hamper the propagation of cracks and hence the thermal shock stability is higher, The property of hydration resistance is improved by zircon addition and the best amount of which is 4%.