OBJECTIVE: To analyze the changes in the respiratory characteristics of the upper respiratory tract under nasal obstruction conditions, to identify the disparities in the flow-heat transfer processes within the respiratory tract, and to provide auxiliary support for the diagnosis and treatment of respiratory diseases. METHODS: We established in this study a three-dimensional (3-D) model of the human upper respiratory tract based on computed tomography (CT) data. Computational fluid dynamics methods were used to compare and analyze the flow and heat transfer characteristics of the human upper respiratory tract under normal breathing and nasal obstructive conditions. RESULTS: During normal breathing, the complex geometric shapes and large areas of heat transfer inside the nasal cavity of humans allowed the respiratory airflow in the posterior part of the nasal cavity to be warmed close to the body temperature. Under unilateral nasal obstruction, relatively high-speed gas and low-speed gas quickly mixed up and homogenized in the posterior part of the nasal cavity, and the airflow underwent sufficient heat transfer in the nasal cavity. Under bilateral nasal obstruction, air was inhaled through the mouth, and the flow velocity was significantly higher at the nasopharynx and the airway entrance compared to that of normal nasal air intake. Moreover, the heat transfer intensity of the airflow in the oral cavity was relatively weak, and the temperature rise of the airflow in the oral cavity was relatively small. CONCLUSION: A stable nasal breathing pattern plays an important role in maintaining human respiratory comfort and preventing respiratory diseases.