<p>To examine the influences of waste polypropylene fiber (PPF) on the strength and internal pore structure of recycled aggregate concrete incorporating iron ore tailings, both the cubic compressive strength and axial compressive strength of the concrete were measured. Additionally, the microstructure was analyzed using scanning electron microscopy. The evolution of pore structure parameters, including pore size distribution, pore type distribution, and nuclear magnetic resonance spectral area in the concrete, was investigated through nuclear magnetic resonance (NMR) analysis. A model correlating the concrete’s pore structure with its macroscopic performance was subsequently developed based on fractal theory. The results demonstrate that an appropriate amount of PPF created a bridging effect that decelerated the progression of macro cracks, enhanced the ductility of the concrete’s failure mode, and increased both cubic compressive strength and axial compressive strength, with the most effective dosage being approximately 0.6%. An appropriate amount of PPF (ranging from 0.3% to 0.6%) facilitated the formation of harmless pores and shifted the pore size distribution towards medium and small sizes. Specifically, a fiber content of 0.6% resulted in the most significant reduction in the T2 spectral area. Furthermore, the pore structure of concrete exhibits distinct fractal characteristics. As the PPF content increased, the fractal dimension initially rose and then declined, demonstrating a strong correlation with the mechanical properties.</p>