Abstract: Using aerodynamic principles for seed sorting, distribution of air flow field is crucial．Aiming at problem of airflow uniformity in agricultural machinery, mainly used centrifugal fan in 5XZ-10 specific gravity sorter as prototype, Solidworks software was used to establish geometric model of centrifugal fan, and Fluent software was used to simulate internal flow field and outlet flow field of centrifugal fan．Through simulation experiments, flow field distribution of centrifugal fan was obtained, and cloud and vector map results of outlet velocity distribution of fan were analyzed, and it was found that internal flow field of fan was disturbed by mechanical structure, and air flow was distributed unevenly at outlet interface of fan, and measures for optimizing flow field of centrifugal fan were proposed, including adding a current collector at inlet of centrifugal fan with double impeller and double inlet, sealing connection between fixed disk and impeller, and improving uniformity of outlet airflow by using a steel plate mesh at fan outlet．Steel plate mesh was installed 0.13 m above fan outlet, and uniformity index of fan outlet airflow was increased from 0.88 to 0.90, and lifting rate was 2.27%, which solved problem of uniformity when air flow provided by fan flows through screen surface of 5XZ-10 specific gravity sorter．