Purpose <p>This review aims to clarify how vibration transfer paths affect accurate fault diagnosis of gearboxes. It addresses three research questions: how transfer paths distort fault-induced vibration signals, how such effects have been modeled in fixed-axis and planetary gearboxes, and how diagnostic methods can mitigate transfer path influences.</p> Methods <p>Existing studies were reviewed and organized according to gearbox type, fault condition, and diagnostic strategy. The review summarizes transfer path analysis and dynamic modeling methods for fixed-axis gearboxes, time-varying transfer path modeling for planetary gearboxes, and transfer path effect elimination methods including sparse decomposition, vibration separation, blind deconvolution, and model-assisted non-blind deconvolution.</p> Results <p>The reviewed literature shows that transfer paths can attenuate fault impulses, modulate signal amplitude and phase, redistribute spectral energy, and introduce multi-path interference and nonlinear distortion. These effects weaken fault features measured by external sensors and may reduce diagnostic accuracy. The influence is more complex in planetary gearboxes because planet gear revolution produces time-varying transfer paths and strong modulation phenomena. Existing methods enhance fault feature extraction, but many rely on phenomenological assumptions or signal-level compensation rather than physically interpretable transfer path reconstruction.</p> Conclusion <p>Vibration transfer paths are a critical factor in gearbox fault diagnosis. Future works are recommended to focus on establishing high-fidelity physical models, revealing compound-fault transfer mechanisms, optimizing sensor placement, and integrating physics-informed diagnostic methods to enhance fault observability, improve diagnostic reliability, and support predictive maintenance.</p>