Abstract: Pot seedling transplanting has the advantages of increasing the production, enhancing the fine grain planting area, and so on.The rice pot seedling transplanting will have a good prospect in the future, but at present the application of rice pot seedling transplanting machine is less in China.Since Japan invented the first transplanter for rice pot seeding in 1900s, large agricultural machinery companies have produced their own models in succession, such as Yanmar and Iseki.The materials and manufacture technologies have been improved through about 40 years' development, but the basic structure and working principle are still kept at the same level.All the transplanting machines use 3 sets of mechanism to complete 3 kinds of movements i.e.picking, transporting and planting.The existing machines have the disadvantages of complex structure, high cost and low efficiency.In order to further improve the rice seedling transplanting quality, the transmission changes with the B spline fitting noncircular gears instead of the eccentric gears.Because the instantaneous transmission ratio of the noncircular gear periodically changes according to a certain rule, the mechanism can achieve constant transmission.Therefore, after the optimization, it is much easier to achieve the ideal trajectory and attitude than the eccentric gear transmission mechanism.Based on the structure of the rice seedling transplanter with double-crank five-bar mechanism, aimed at the important driving part, this study has developed the simple transplanting mechanism for rice pot seedling based on B spline fitting curve, i.e.transplanting mechanism with fitting gear five-bar for rice pot seedling.Transmission analysis for fitting gear pitch curves of the mechanism is carried out and the kinematic model of transplanting mechanism is established.A computer-aided analysis and optimization software of the transplanting mechanism with fitting gear five-bar for rice pot seedling is developed on the Matrix Laboratory GUI platform.Through tuning the data points by man-machine interaction, the pitch curve of noncircular gear is optimized and the structural parameters are obtained, which can meet the demand of track and attitude in the transplanting process for rice pot seedling.In entity modeling module, the three-dimensional (3D) model of transplanting mechanism parts is built, the components are assembled, and the interference checking of 3D model assembly is finished.Then, the two-dimensional (2D) engineering drawings are generated.The virtual prototype simulation is carried out by the automatic dynamic analysis of mechanical systems, and the simulation results initially showed the design of mechanism is rational.The core component of transplanting mechanism is machined, and then fit together and used for experimental study on the test shelf.Through the bench test, the rationality and effectiveness of the parameters of transplanting mechanism are validated.In the process of pot seedling transplanting, the excessive transplanting frequency will make the seedling damaged, broken or thrown out, and on the contrary it will affect the operation efficiency.Therefore the selection of suitable transplanting frequency plays an important role in the process of pot seedling transplanting.Taking the pincette opening span, the grasping force of pincette and the pinching frequency as factors, the damaged seedling rate and the missed seedling rate in hill as evaluation indices, the quadric regression orthogonal revolving combination experiment is conducted.By using the Design-Expert 7.0 software, the analysis results further verify the design of transplanting mechanism with fitting gear five-bar is reasonable.