<p>Seismic safety evaluation for loess ground is often tailored to local conditions, yet the influence of regional soil variability on dynamic parameters is seldom rationally addressed. This study investigated the correlation between clay activity, a synthetic physical index characterizing soil variability, and dynamic properties of intact loess, with microstructural and water-retention evidence derived from dynamic triaxial tests, water-retention tests, and scanning electron microscopy (SEM) analysis. Results show that the backbone curve rises with lower clay activity, corresponding to higher dynamic shear modulus and lower damping ratio. The Hardin-Drnevich model was modified by incorporating a power relationship between reference strain and clay activity. Quantified microstructural indexes indicate that the closer the particle morphology approaches sphericity, the smoother the pore edges, and the more uniform the pore distribution, the higher the initial dynamic shear modulus <i>G</i>_d0 and maximum damping ratio <i>λ</i>_max, corresponding to higher clay activity. The above microstructural morphology, rather than matric suction, exerts far greater influence on <i>G</i>_d0, while <i>λ</i>_max is positively linked to matric suction or negatively to clay activity. The above preliminary results demonstrate the correlation between clay activity and dynamic behavior of intact loess and hold potential significance for seismic safety assessment of loess grounds.</p>