Abstract: Abstract: Based on the combination of agricultural machinery and agronomic requirements, bowl dish precision seeder for rice must guarantee 3~5 rice seeds dropped into a hole. For this reason, researching on motion law and revealing the investment mechanism of bowl dish precision seeder for rice in dropping process can help improve the dropping rate and reduce the damage rate of bowl dish precision seeder for rice. The second Lagrange multiplier can be used to describe the dynamics of mechanical systems with highly uniform rules in the theory, methods, forms and application. The second Lagrange multiplier provides the programming method for solving the dynamic problems of a unified system. The method not only has important theoretical significance and practical value in mechanics, but also provides the physical idea and mathematical skills necessary for the study of modern physics. As a consequence in this paper, based on the dynamics analysis, the dynamics model of bowl dish precision seeder for rice in the dropping process was established by the second Lagrange multiplier. To obtain relationship between resultant velocity and displacement of bowl dish precision seeder for rice in dropping process, the dynamics model was simulated by Matlab with the parameters that the cylindrical hole diameter is 10 mm, the shaped hole thickness of 4 mm, the material of the flap is polycarbonate, the length of the flap is 14 mm, the heavy of the flap is 0.82 g, varieties of rice is Kongyu 131, and kilo-grain weight is 39 g. The results show that characteristics of rice motion on dropping process are affected by certain factors such as flap length, shutter quality, and rice quality. The rice velocity presents nonlinearly increase with the displacement. At the beginning, the rice moving more slowly, rate of increase becomes large with the displacement increases. When the actual displacement is 27 mm, rice velocity is 0.54, 0.45, 0.34, 0.29 and 0.18 m/s respectively. In the same conditions，the process of dropping of bowl dish precision seeder for rice was photographed on line by the high-speed photography, and the relationship between resultant velocity and displacement of bowl dish precision seeder for rice in dropping process was obtained. Compared with the theoretical results, it shows that the general trends of rice are the same. In the first place, rice moving more slowly, rate of increase becomes large with the displacement increases. When the actual displacement is 27 mm, rice velocity is slightly different, which is 0.5, 0.42, 0.32, 0.26 and 0.17 m/s respectively. The similarity degree is greater than 90% with a gentle curve of speed, no fluctuation by simulation, nonetheless the fluctuation by the high-speed photography. The results show that rice seeds in the actual dropping process can be affected by many inevitable factors, such as rice attitude change, data collection error in the dropping process and so on. The results can provide a theoretical foundation for improving the dropping rate of precision sowing device in rice seeding bowl.