The use of crushed rock sand (CRS) as a substitute for natural sand is a necessary and feasible approach to address depletion of natural sand resources. This study investigated the effect of CRS aggregate gradation, based on Talbot grading theory, on pore structure and mechanical properties of mortar. 10 CRS mortars with different Talbot gradations were prepared, and quantitative relationships between Talbot gradation, pore characteristics (size distribution, fractal dimensions, and pore connectivity), acoustic emission (AE) characteristics, and compressive mechanical properties were analyzed using nuclear magnetic resonance (NMR) and AE techniques. The optimal Talbot index value was determined to be 0.4, based on the observed changes in pore structure and mechanical properties. Furthermore, the influence of Talbot index on internal damage process of CRS mortar was analyzed in conjunction with AE characteristics, and a prediction model for mortar strength was established based on porosity and AE cumulative counts. The correlation between pore structure, AE characteristics and mechanical properties of CRS mortar under Talbot grading was systematically investigated, which provides theoretical support for optimal design of CRS mortar materials. The application of Talbot grading theory in design of mortar is explored to provide a scientific basis for improvement of mortar engineering performance.