In the factory rice cell seedling, dropping process of rice seed metering device affects the seeding performance. To meet the requirement of the rice seed metering device, rice seed movement discipline and mechanism in the dropping process were analyzed theoretically. Dropping process was divided three parts: timely dropping process, delayed dropping process, and enforcement dropping process. The relationshipbetween cell tray velocity and the parameters of seed metering device was derived. Dropping process was analyzed based on high-speed photography technology. Analysis of dropping process provided a basis for the establishment of seed metering device design theory and optimal design. The relationship between the type hole length and the parameters of seed metering device was established. Analysis showed that rational parameters of metering device could ensure seed won’t have wall-type collision with the other side. 