Abstract: Abstract: Seeding uniformity is a very important index in the air-assisted centralized metering device. Gas-solid two-phase flow including seeds and airflow exists in seed feeding device, seed delivering tube, pressurized tube and distributor. In order to study effects of pressurized tube's structure on seed distribution uniformity in the air-assisted centralized metering device, a numerical study of gas-solid flow in pressurized tube was carried out by the coupling approach of discrete element method (DEM) and computational fluid dynamics (CFD). Effects of structural parameters including dimple depth, dimple pitch and pressurized tube's length on seed motion, distribution uniformity and airflow field were studied. The variation coefficient of seed distribution and variation coefficient of seeds' distribution uniformity were utilized to evaluate seed distribution. The mathematical models were set to describe structural parameters and seed distribution uniformity by means of the design of the regression-orthogonal combination. Besides, effects of pressurized tube's length and airflow pressure on seed distribution uniformity were analyzed using bench experiments. Results showed that: 1) The air-assisted centralized metering device with pressurized tube increased variation coefficient of seed distribution and decreased seed velocity and variation coefficient of seeds' distribution uniformity. Pressurized tube's length, dimple depth, interaction between dimple depth and pressurized tube's length affected variation coefficient of seeds' distribution uniformity significantly. The optimum parameters combination was dimple depth of 4.2 mm, dimple pitch of 15 mm and pressurized tube's length of 180 mm, which was achieved by the method of multi-objective programming problem function. Under the superior combination of structural parameters, the variation coefficient of seed distribution and the variation coefficient of seeds' distribution uniformity were 91.17% and 4.91%, respectively. 2) Airflow velocity field in pressurized tube and seed motion characteristics were obtained by analyzing gas-solid flow status. Airflow velocity and pressure in peak of pressurized tube had the minimum value and the maximum value, respectively. Otherwise, airflow velocity and pressure in trough of pressurized tube was the maximum and the minimum, respectively. The peak surface of pressurized tube was located in high pressure and low airflow velocity zone and trough surface of pressurized tube was located in high airflow velocity and low pressure zone. The alternate high and low airflow pressure in pressurized tube changed airflow field distribution. Seed velocity and force in pressurized tube had the trend of sine. 3) Bench experiments indicated that the ranking order of the factors affecting variation coefficient of seeds' distribution uniformity was: airflow pressure > pressurized tube's length for rapeseed and pressurized tube's length > airflow pressure for wheat. Based on the optimized structural parameters and airflow pressure of 1 200 Pa for rapeseed and 1 600 Pa for wheat, variation coefficients of seeds' distribution uniformity were 2.84% and 2.89%, respectively. Results suggest that the optimization of structural and working parameters of pressurized tube can improve seed distribution uniformity. The investigation of airflow field, seed movement and seed distribution uniformity involved in this research may contribute to optimizing pressurized tube's structure and analyzing seed movement mechanism.