Carbonate reservoir seepage channels are dominated by fractures, which are mostly modified by acid fracturing technology. However, after acid-etching, the rock structure on the fracture surface is destroyed and then softened and formed an acid-etching softened layer, which reduces the mechanical properties of the rock and leads to a decrease in the support strength of the acid-etched fractures, affecting the fracture conductivity. At present, there are fewer researches on the acid-etching softened layer, for the understanding and insufficiency of the existing research, this paper studies the micro-morphology, pore structure, mechanical properties and its influencing factors of the acid-etching softened layer of carbonate rock from the aspects of acid-rock reaction kinetics, etching morphology, microstructure characterization and mechanical properties. The experimental results show that there exists a certain thickness of softened layer is on the surface of the rock after acid-etching, which led to a decrease in the surface hardness and compressive strength of the rock, while the temperature and the concentration of the acid are the dominant factors affecting the formation and distribution of the softened layer. Due to the existence of the softened layer, the acid is more likely to break through the rock surface and form a large number of inhomogeneous dissolution pores inside the rock, which changes the pore structure and distribution in the rock, and seriously affecting the mechanical properties of the rock. This study further clarifies the formation mechanism of the acid-etching softened layer and the changing law of its mechanical properties, which can provide theoretical basis and reference for the optimal design of acid-etching fractures in deep carbonate reservoirs.