At present, precision sowing of small grain crops is a difficult problem, millet is a representative crop. An air-suction precision hill-drop seed-metering device was designed to seed coated millet to solve the problem of the seed-suction hill blockage and seed damage. Three seed-metering device models with different diameter hills 1.6, 1.8, and 2.0 mm were simulated and calculated by ANSYS FLUENT. The comparative analysis of the pressure nephogram and the airflow velocity vector illustration. The results showed that the airflow field of the seed-metering device with a 1.6 mm diameter hill was beneficial to the stability and uniformity of sucking and planting seeds. The main structure and operation parameters in terms of negative pressure in the air chamber, rotation speed of the seed-metering device, and diameter of seed-suction hill were determined by theoretical analysis. Orthogonal test was carried out through the JPS-12 seed metering device test bench, the coated millet variety 8311-14 was selected as the test object. The qualified index of seeds number per hill, qualified index of hill spacing, index of empty hill, and coefficient of variation for hill spacing were chosen for evaluating the working performance. The results of orthogonal test showed that, the diameter of seed-suction hill was 2.0 mm, the negative pressure was -0.8 kPa, the rotation speed of the seed- metering device was 30 r/min. What’s more, a regression model based on the orthogonal test results was established, qualified index of seeds number per hill was 86.67%, qualified index of hill spacing was 89.33%, index of empty hill was 1.33%, and coefficient of variation for hill spacing was 13.74%. Notably, the working performances of the device can meet the requirement of precision hill-drop of millet seed.