Current rice potted-seedling production line fails to achieve full automation, especially the separation and supply of potted-seedling tray. A set of combined type rice potted-seedling tray consisting of a soft potted-seedling tray and its supporting hard tray was proposed, and an automatic assembly line was developed. The assembly line consisted of a separation mechanism for soft potted-seedling tray based on finger-clamp vacuum suction cup and a separation mechanism for hard tray based on linkage mechanism combined with a lifting platform, and by combining them to form a tray embedding mechanism. A vacuum suction cup was designed to be installed symmetrically through hinges to mimic the grasping action of human fingers. The vacuum adsorption method was used to clamp the soft potted-seedling tray without damaging the surface of the soft potted-seedling tray. The diameter of vacuum suction cup was determined to be 8mm through calculation. ANSYS was used to analyze the horizontal deformation of the soft potted-seedling tray when it was adsorbed and lifted by the vacuum sucker, and eight groups of vacuum suckers were determined and the reasonable layout was carried out to ensure that the deformation of the soft tray during lifting was less than 1mm. The results of simulation and practical test verified the feasibility of the design. The kinematics analysis of the linkage mechanism was carried out by using ADAMS, and the optimal lifting height of the lifting platform and the opening and closing angle of the connecting rod were determined. Therefore, the cylinder stroke used by the hard tray separation mechanism was selected as 30mm. The control system of the whole machine was designed, and the movement of the whole machine was realized by the combination of stepping motor and cylinder. Through the analysis of motion flow and timetable, the travel switch was selected as the common signal of the two parts of the mechanism to carry out appropriate timing distribution and ensure the highest efficiency. The overall machine was modeled using SolidWorks. Based on the machine model, the prototype was manufactured, and the experiments of separating and embedding tray were carried out. 220V single-phase alternative current was used to power the air compressor and the prototype machine. The pressure regulating valve of the main pneumatic circuit was set to be 0.45MPa. The experimental results showed that the success rate of the hard tray separation mechanism was 97%, and the efficiency was 1000 trays/h. The success rate of separation mechanism for soft potted-seedling tray was 94.25%. When the speed of separation and embedding tray was 600 sets/h, the success rate was 93.25%. The assembly line ran smoothly, and there was no cumulative deviation in multiple tests, which met the working requirements of the rice seeding line.