This study investigates the pore structure and fractal characteristics of manufactured sand aggregate (MSA) mortar using 1H low-field nuclear magnetic resonance (LF-NMR) relaxation methods. The research focuses on the evolution of pore structure and fractal characteristics in MSA mortar under long-term water saturation. Five single-graded mortars and one synthetic-graded mortar were prepared, and their porosity, pore gradation, pore connectivity, and pore fractal dimension were analyzed. The surface-to-volume ratio (SVR) of the aggregates was used to characterize the gradation. The results show that MSA has a fresh rock interface with fewer pores, leading to higher compactness and lower porosity. The SVR of the aggregates positively correlates with the porosity of the mortar. Long-term water saturation increases the porosity of the mortar, particularly in the micropore range, indicating further hydration reactions. The permeability of single-graded mortars increases with the SVR, while synthetic-graded mortars exhibit enhanced impermeability and corrosion resistance. Fractal analysis using three methods (F-sv, F-T2c, and F-ps) reveals that the pore structures exhibit favorable fractal characteristics, with the fractal dimension increasing with the SVR. The study establishes a correlation model between pore structure parameters and aggregate SVR, providing insights into the pore distribution evolution and engineering permeability evaluation of MSA mortar.This study investigates the pore structure and fractal characteristics of manufactured sand aggregate (MSA) mortar using 1H low-field nuclear magnetic resonance (LF-NMR) relaxation methods. The research focuses on the evolution of pore structure and fractal characteristics in MSA mortar under long-term water saturation. Five single-graded mortars and one synthetic-graded mortar were prepared, and their porosity, pore gradation, pore connectivity, and pore fractal dimension were analyzed. The surface-to-volume ratio (SVR) of the aggregates was used to characterize the gradation. The results show that MSA has a fresh rock interface with fewer pores, leading to higher compactness and lower porosity. The SVR of the aggregates positively correlates with the porosity of the mortar. Long-term water saturation increases the porosity of the mortar, particularly in the micropore range, indicating further hydration reactions. The permeability of single-graded mortars increases with the SVR, while synthetic-graded mortars exhibit enhanced impermeability and corrosion resistance. Fractal analysis using three methods (F-sv, F-T2c, and F-ps) reveals that the pore structures exhibit favorable fractal characteristics, with the fractal dimension increasing with the SVR. The study establishes a correlation model between pore structure parameters and aggregate SVR, providing insights into the pore distribution evolution and engineering permeability evaluation of MSA mortar.