As a major granite production area, Hezhou in Guangxi generates a large amount of granite rock powder waste during mining and processing, posing significant resource waste and environmental threats. This study focuses on abandoned granite powder in Hezhou. Using Portland cement as a curing agent, the granite powder is treated with different cement contents and curing ages. Unconfined Compressive Strength (UCS) tests are conducted, and microstructural analyses (XRD and SEM) are performed to investigate the mechanical properties and cementation mechanisms. The results show that the compressive strength peaks when the cement content is between 4 and 6%, and the UCS reaches its optimal value at curing ages of 7–14 days. The strength of the cemented granite powder increases with higher cement content, attributed to the strong positive correlation between the intensity of C-S-H characteristic peaks and cement content, which enhances cementation and soil compaction, thereby significantly improving strength. A predictive formula for UCS is developed, incorporating cement content, curing age, and void ratio. These findings provide a theoretical basis for the resource utilization of solid waste materials.