In order to improve the quality of the seed metering device under the condition of high slope and incline, a horizontal disc maize precision seed metering device for hilly land was designed. Based on the analysis of the factors affecting the performance of the horizontal disc seed metering device, the inclined holes with different end surfaces and the ring-shaped shell which divided into regions were designed, the key structural parameters were determined. The double-sided seed filling slopes of the disc were designed to improve the fluidity and seed filling performance of the seed group. With the small end surface diameter of the hole, the seed guide slope angle, and the rotation speed of the seed disc as the test factors, the qualified index, the missing index and the multiple index as the evaluation indexes, the quadratic orthogonal rotary regression combination test was carried out and the parameters were optimized. The results showed that when the small end surface diameter was 11.25 mm, the seed guide slope angle was 57.43°, and the rotation speed of the seed disc was 10.56 r/min, the qualified index was 94.77%, the missing index was 1.47%, and the multiple index was 3.86%, which met the requirements of precision seeding. Under the optimized parameters, the performance test of the seed metering device under the inclined condition was carried out (the inclination directions were forward, backward, left and right, and the inclination angles were 6°, 12° and 18°). The results showed that compared with the disc without a filling slope, the disc with a double filling slopes no matter the inclination angle directions or angles were changed (0°~18°), the qualified index of the seed metering device was greater than 93%, and the missing index was less than 4%, and the difference was small. The seed metering device can provide references for the development and application of maize planter in hilly and mountainous areas.