The exploration and development of oil and gas are gradually expanding from shallow to deep/ultra deep reservoirs. Deep and ultra deep layers have become more and more important for increasing oil and gas storage and production. Limited by the drilling depth and experience at 20th century, the curing stress of traditional cements strength testing was only 20.7MPa. The pressure is extremely high in deep and ultra deep wells, so the compressive strength and strength development time of cements in downhole may be different from that obtained from laboratory. The inaccurate design of the compressive strength and strength development time of cements may lead to poor bonding quality or sustained casing pressure. In this paper, the strength development time, compressive strength, scanning electron microscopy, porosity, permeability, X-ray diffraction patterns, and microstructures under different curing stress were obtained. The increasing of curing stress can effectively improve the strength of cements.