The crystalline quality of two SrTiO3 substrate wafers has been analyzed by X-ray double crystal rocking curve and topography.The surface structures of these two samples are investigated by grazing X-ray specular reflectivity and diffuse scattering.Results show that there are mosaic defects in both samples,but the crystalline quality of one sample is relatively high.There is big difference in the surface structures of these two samples.The root mean roughness σ of one sample is only (0.5±0.1)nm,while the other one is as high as (1.3±0.1)nm.The lateral correlation length of one sample is (1200±200)nm,but another is (300±20)nm.The rough surface will enhance the X-ray diffuse scattering and reduce the specular reflectivity.The substrate wafer with higher crystalline quality has also a relative smooth surface and is suitable for epitaxial growth.