Abstract: To explore the micro-mechanical and damage characteristics of coal under load, this study conducted stepwise loading and unloading small-angle X-ray scattering (SAXS) experiments using a self-developed micro-loading system and an in-situ synchrotron radiation SAXS experimental station. The SAXS experimental data were used to analyze the damage evolution of nanopore structures in coal during the stepwise loading and unloading process, and the damage mechanisms of the microstructures of open and closed pores in coal were discussed. The research results indicate that the stepwise loading-unloading SAXS experiments of coal samples consistently exhibited Porod positive deviation. Different loading methods did not alter the intrinsic Porod deviation pattern of the coal, but external loading had a significant impact on the scattering intensity. The surface fractal dimension, pore fractal dimension, specific surface area, and porosity of nanopore structures in coal samples exhibit dynamic changes, increasing initially, then decreasing, and finally increasing significantly with the increase of loading. Based on these staged changes, the damage process of nanopore structures under stepwise loading-unloading conditions is divided into three stages: minor damage stage, compression stage, and fracture stage. In addition, the influence of uniaxial loading and stepwise loading-unloading on the damage mechanism of nanopores was analyzed based on the variation patterns of the microstructure. It was revealed that stepwise loading-unloading exacerbates pore closure, structural collapse, and through-breaking processes. Furthermore, the failure and disaster mechanisms of nanopores under loading-unloading conditions were discussed for both gas-bearing and non-gas-bearing coal. These findings provide new insights into the micro-damage mechanisms and disaster-causing mechanisms of coal under cyclic loading and unloading.