Abstract: Quality of seeds directly affects grain production, and screening of excellent seeds is of great significance to national food security．A univariate test was carried out on problem of uneven airflow distribution on sieve surface of 5XZ-10 specific gravity seed sorter．Using Fluent software, method of combining numerical simulation and experiment was used to solve flow field of heavy separator．To simplify amount of calculation, a porous media model was introduced instead of an airflow orifice plate．Parameters of porous medium model were solved by numerical fitting, geometric model of air chamber was established and feasibility of model was verified．Height scale coefficient of airflow orifice plate arrangement was α as a univariate to obtain distribution characteristics of airflow field and aerodynamic field of sorter．To obtain a reasonable airflow of sieve surface, effect of different airflow orifice heights on airflow stability and uniformity of air chamber outlet interface was discussed, and it was found that when α=0.84, airflow stability and uniformity of air chamber outlet interface was good．Reasonable installation height of airflow orifice plate was determined to be 530 mm, which provided experimental data and a theoretical basis for optimal design of a specific gravity seed sorter．