It is often necessary to adjust the planting frequency and the speed of dryland trasplanters at the same time to meet the agronomic requirement of planting. An eightlinkage transplanter，consisted of crankrocker mechanism, parallelogram amplification mechanism, swing slide mechanism and opening and closing mechanism，was designed to solve this problem. The mechanism of this eightlinkage transplanter was analyzed, and the motion model was also established. The influence of length on the verticle displacement, motion trail, velocity and acceleration of the mount point was researched. The influence of limit position angle and rocker swing angle were also researched. The optimized length of linkages were calculated by using Matlab GUI. And the finally length of linkages were l1=39mm，l2=42mm，l3=152.04mm，l4=153.6mm，l5=40mm，l6=30mm，l7=100mm，l8=154mm. According to the results of field experiments, the excellent rate of plant erectness could reach 94%, the total qualified rate could reach 96%, and the coefficient of variation of plant spacing could reach 3.25% by using the optimum length of levers. It could conclude that the eightlinkage planter had a good planting performance and could meet the agronomic requirements. 