Semiconductor saturable absorber mirrors （SESAMs） are vital for enabling ultrafast fiber lasers， yet their mode-locking performance is often constrained by recovery time and nonlinear absorption parameters. Current optimization studies on SESAM mode-locking properties mainly focus on structural and material parameters of the quantum well absorption layer， while systematic research on the directional influence of a key fabrication parameter—the substrate miscut angle during epitaxial growth—remains scarce. This study presents the first systematic investigation into the impact of substrate miscut angles （0°， 2°， and 6° toward the ［110］ direction） on the structural properties of epitaxially grown InGaAs/GaAsP SESAMs and their mode-locking characteristics， revealing the regulatory effect of different substrate miscut angles on SESAM performance. Comprehensive characterization via high-resolution X-ray diffraction （HRXRD）， atomic force microscopy （AFM）， photoluminescence （PL） spectroscopy， and spectrophotometry reveals that increasing the miscut angle introduces lattice defects， significantly shortening recovery time. However， larger miscut angles also increase surface roughness and nonsaturable losses， degrading nonlinear absorption. In the mode-locking experiment of a Yb-doped fiber laser， SESAMs with the 2°-miscut angle achieved stable mode-locking， outputting 8.2 ps pulses at 1064 nm， while the 6°-miscut sample exhibited deteriorated mode-locking performance due to material quality degradation. This work fills a critical gap in understanding how the substrate miscut angle influences SESAM mode-locking properties， providing a new optimization dimension and theoretical foundation for designing high-performance ultrafast lasers.