Abstract: This study investigates the mechanical behavior, deformation characteristics, and damage evolution mechanisms of argillaceous quartz siltstone under cyclic-monotonic loading conditions. Through cyclic-monotonic loading tests conducted at varying upper-limit loads and cycle numbers, complemented by three-dimensional digital image correlation (DIC) and acoustic emission (AE) monitoring, the strength evolution, heterogeneous deformation behavior, and crack propagation processes of the rock were systematically analyzed. The results indicate that the strength and deformation heterogeneity of the rock are significantly influenced by the number of cycles and the upper-limit load. Under low-cycle conditions, initial damage mechanisms such as pore compaction and micro-crack closure dominate. With increasing cycle numbers, localized deformation and crack propagation become more pronounced. Using DIC technology, the spatiotemporal evolution of the surface strain field was quantitatively characterized, and a heterogeneity assessment method based on the high strain area ratio (HRAR) and heterogeneity index (Hj) was proposed. AE ringing count variations exhibited strong consistency with the heterogeneity evolution, showing a sharp increase with accumulating cycles, which reflects the progressive accumulation and localization of rock damage.