Olfactory dysfunction is a common functional problem in nasal diseases or after nasal surgery. Its mechanism is closely associated with airflow distribution and the transport and absorption of odorant molecules in the olfactory cleft region caused by changes in nasal structure. Most existing studies based on computational fluid dynamics have focused on local structure or single physical variable, and a systematic evaluation of olfactory function is still lacking. To address this problem, a multi-layer olfactory function evaluation system is established.? Numerical simulations are performed to investigate airflow characteristics in the nasal cavity and mass transfer processes in the olfactory cleft region for a case of olfactory cleft enlargement surgery. The evaluation system is constructed from three levels, including the anatomical structure level, the nasal airflow level, and the odorant mass transfer level. The effects of nasal structural changes on ventilation conditions and wall mass transfer characteristics in the olfactory cleft region are analyzed comprehensively. In addition, the olfactory cleft flow ratio and the olfactory cleft contribution ratio are introduced to quantitatively evaluate the functional role of the olfactory cleft region in the nasal cavity. The results show that postoperative structural adjustment not only improves the local morphology of the olfactory cleft region, but also significantly enhances airflow supply and mass transfer in this region by optimizing the overall airflow distribution, which provides a theoretical basis for nasal dynamics in improving olfactory function. It is concluded that the proposed multi-layer olfactory function evaluation system effectively correlates structural changes in the nasal cavity with olfactory functional performance, and offers a feasible quantitative method for olfactory-related nasal structure optimization and postoperative functional evaluation.