This paper presents a photonic crystal (PhC) line-defect slow-light waveguide modified by resonant rings. We introduce resonant rings into the line defect, constructing a slow-light waveguide with high normalized delay bandwidth product (NDBP) and low group velocity dispersion (GVD). We simulate, analyze, and optimize the structural parameters of this slow-light waveguide using the finite difference time domain (FDTD) method, theoretically achieving a maximum group index of 3.7, maximum bandwidth of 15.6 nm, and maximum NDBP of 0.441 6 for slow-light effect. The resonant ring-modified PhC slow-light waveguide designed in this paper exhibits GVD lower than the order of 10-20 s2/m over a normalized frequency range from 0.355 4 to 0.417 5. This study is expected to provide theoretical references for the study of slow-light buffering devices based on PhCs with high NDBP values.