A new compound Sr2CaMoO6 has been synthesized by solid stare sintering. The phase transition of this compound was investigated by means of DTA, X-ray powder diffraction, precise measurement of lattice parameters and other methods. It is discovered that the compound has a displacive phase transition of the first order at (767±5)℃. The low temperaiure phase, or Sr2CaMoO6, belongs to orthorhombic system, with space group Pmm2, its lattice parameters at room temperature are:a = 8.1933?, b = 5.7611? and c=5.8410?, the measured density is Dm= 4.97g/cm3, and each unit cell contains two formula weight. The high temperature phase, β-Sr2CaMoO6, belongs to the cubic system, with space group Fm3m and the lattice parameter is α = 8.281? at 800℃; Z = 4. The calculated density is Dx= 4.76g/cm3.The crystal structures of α Sr2CaMoO6 and β-Sr2CaMoO6 was also determined by means of the X-ray polycrystal diffraction method. The character of the structure and the factors influencing phase transition temperature are discussed.