There are great difficulties in sowing green manure in paddy fields before rice harvest and in hilly and mountainous areas. These problems mainly include sowing equipment cannot work in the field and the labor intensity of manual sowing is high. Based on the agricultural multi rotor unmanned aerial vehicle platform, a centrifugal disc type green manure seed broadcast sowing device was developed, which can be used to sow seeds such as Chinese milk vetch and Orychophragmus violaceus. The device can be easily and quickly assembled and connected with unmanned aerial vehicle platform. It was mainly composed of hitch mechanism, seed box, seed metering mechanism, broadcast sowing mechanism and sowing automatic control system. The screw conveying seed metering mechanism was used to achieve continuous and stable quantitative seed metering. After the broadcast sowing mechanism was optimized, the seeding was more uniform and smooth. The control system can follow the unmanned aerial vehicle flight speed to control the seed amount of the seed metering mechanism, and set the rotation speed of the seed-rotating disc for broadcast sowing mechanism according to different varieties of green manure seeds, so as to complete the quantitative seeding and uniform sowing of different varieties of green manure. The seed of milk vetch, a typical green manure variety, was selected as the test object. Three-factor and three-level orthogonal performance test was carried out with setting variation coefficient of sowing uniformity Y1 and relative error of sowing rate Y2 as the evaluation indexes, rotation speed of the auger for seed metering mechanism A, rotation speed of the seed-rotating disc for broadcast sowing mechanism B and flight speed C as the influence factors. According to the results of orthogonal test, rotation speed of the auger for seed metering mechanism A and rotation speed of the seed-rotating disc for broadcast sowing mechanism B had extremely significant influence on the two evaluation indexes, flight speed C had significant influence on the two evaluation indexes. The importance order of the factors which affected the Y1 was B，A and C, and affected the Y2 was A，B and C, the optimal combination of working parameters was A2BC2, A was 190r/min, B was 1700r/min, C was 5m/s, and Y1 was 28.47% , Y2 was 11.81%. The field experiment under the optimal combination of working parameters showed that the seedling emergence was good. The research result provided a theoretical basis for improving the green manure broadcast sowing device based on unmanned aerial vehicle platform, and provided equipment support for large-scale promotion of green manure planting.