<p>To address the resource utilization of waste stone powder (WSP) and expand its application pathways, this study focuses on the insufficiency of damage constitutive models considering damage factors in the initial loading stage and under multi-factor conditions for concrete. The aim of this paper is to investigate the influence of waste stone powder on the mechanical properties of alkali-activated concrete, with waste stone powder replacing slag and fine aggregate as research parameters. Through uniaxial compression tests on specimens, the variations in mechanical performance characteristics were comparatively analyzed. The results indicate that the concrete mainly exhibits typical splitting failure. As the replacement of fine aggregate with waste stone powder increases from 10 to 50%, the deformation performance of the specimens improves. The axial strain–hoop strain curves of the specimens show a bilinear variation, and the curve equations were fitted using piecewise functions, with R² values ranging between 0.927 and 0.999. For specimens with waste stone powder replacing slag, the axial peak stress fc0 decreases with increasing replacement content. In contrast, for specimens with waste stone powder replacing fine aggregate, the peak strain gradually increases with higher replacement content, and the peak stress does not show a significant reduction, although the lateral deformation performance deteriorates. The specimen with 30% waste stone powder content exhibits the highest peak stress <i>f</i>_<i>c0</i> and demonstrates the best mechanical performance compared to other specimens. Furthermore, a plastic damage constitutive model considering the plastic deformation and energy dissipation of the material was proposed, and the accuracy of the model was validated. This study provides data and theoretical foundations for promoting the practical application of alkali-activated slag concrete incorporating waste stone powder in engineering projects.</p>