Computer aided optimization of cement-based materials proportion can accurately quantify the accompanying microstructure evolution, material composition, and the mechanical properties changes. However, no relevant research exists on the effect of cement hydration on cemented paste backfill (CPB) strength using numerical simulation considering above mentioned aspects. This study builds a numerical model based on continuous damage mechanics methods considering CPB hardening process per the particle size distribution (PSD) of tailings, the known determined strength characteristics of components, and the existing cognition of cement hydration mechanism. A series of CPB mechanical properties simulation was then carried out. The relations and influencing factors between CPB's hardening process and mechanical parameters were obtained. Results have showed that numerical simulation can more intuitively show the relationship between the crack development and PSD of CPB's hardening process at different stages under external load, and can quantitatively analyze the influence of strength properties. The strength development during CPB hardening is the combined result of matric suction and hydration products. The smaller the solid content, the more prominent the matric suction during hardening. The greater the binder content, the less the effect of matric suction on strength. The binding ability of cement hydration products to tailing particles is linked with the spatial distribution of tailing particles. The tailings gradation plays a key role on CPB's strength characteristics. The heterogeneous distribution of CPB strength can be configured by analyzing the non-uniform distribution of hydration degree in CPB's hardening mechanism. Accordingly, the proposed framework can not only provide theoretical guidance for the preparation and application of CPB, but also can save the cost and interminable time of laboratory tests and reduce the uncertain factors caused by environmental conditions.