Abstract: Abstract: In order to improve the status quo that mechanical direct seeding level for cotton is insufficient in the Yellow River basin, a kind of inside-filling precision seed-metering device with stepped filling holes which can reduce the shearing damage on seeds and blocking of nest inside hole was designed. To realize stepless adjustment of the seeding rate, a composite seeding plate which consists of inner seeding plate, lug and outer seeding plate assembled by bolts and nuts was adopted. This paper set forth the working principle of inside-filling seed-metering device and determined the general structure along with necessary parameters of key components. The cotton seed variety E`kangmian-10 with moisture content 11.01% (wet basis) was selected as experimental object. Before testing, all of the cotton seeds had been delinted and coated, and there were no damaged cotton seeds after manual selection. In bench test, the single factor experiment was performed on the seed-metering device. The factor was the shape of filling hole which was changed by replacing lugs, so as to study the effect of shape of filling hole on seeding performance and the optimal one was used for cotton direct seeding. Based on pre-experiments, the nest inside hole depth, seed entrance height and seeding plate rotational speed were taken as main impact factors and the qualified rate, reseeding rate, miss seeding rate and damage rate of seeding were taken as the test indexes. Then quadratic regression rotation-orthogonal combination experiment with concave filling hole was executed. The regression model was established and the influence law of various factors on test indexes was analyzed. Through the tests above, the optimal combination of each factor was obtained. The results indicated that the structural design of anti-injury was reasonable due to the low damage rate, and the concave filling holes are more suitable for cotton direct seeding than straight and convex filling holes. Due to its small volume and the incapability of cotton seeds filling into the hole smoothly under the application of gravity, centrifugal force and interaction force of cotton seeds, the convex filling hole adopted in the inside-filling seed-metering device was seriously blocked which resulted in a high miss seeding rate, the miss seeding rate decreased and qualified rate increased with the increasing of filling hole volume for straight filling hole and the phenomenon of blockage still existed, and seeding performance reached the optimal state without blockage for concave filling hole. The order influencing qualified rate of seed-metering device was seeding plate rotational speed>nest inside hole depth>seed entrance height, and the order influencing miss-seeding rate of seed-metering device was nest inside hole depth>seed entrance height>seeding plate rotational speed. The optimal combination was nest inside hole depth with 7.7 mm, seed entrance height with 62.9 mm, seeding plate rotational speed with 23.52 r/min. On the condition above, the qualified rate (1-3 seeds per hole), reseeding rate (more than 3 seeds per hole), miss seeding rate (0 seed per hole) and damage rate of seeding were 96.23%, 1.92%, 1.85% and 0.17%, respectively. In order to test the seeding performance of seed-metering device in the field, the field experiment was carried out and the results showed that the qualified rate was 95.44%, reseeding rate was 2.28%, miss eeding rate was 2.28%, damage rate was 0.06%, the qualified rate of hole distance was 97.63% and the variation coefficient of hole distance was 23.11%, which meet agronomy requirement for cotton direct seeding. The study provide a reference for the structural design and optimization of inside-filling precision seed-metering device for cotton.