To realize the efficient utilization of sludge incineration ash (SIA), this study started with the influence of SIA on the particle accumulation state and mechanical properties of cementitious materials. The influence mechanism of SIA on hydration process and microstructure was analyzed by hydration heat, XRD, TG-DSC, MIP and SEM-BSE. The results show that the irregular morphology and high absorption characteristics of SIA have a negative impact on cement fluidity. Although the particle size distribution of SIA is wide, the continuous distribution characteristics can be used to improve the overall packing density of the cementitious material system. However, high content (30%) of SIA reduces the cement performance due to its porous properties and dilution effect. This study provides a theoretical basis and data support for the application optimization of SIA in building materials.