To improve the automation and efficiency of plug seedling transplanter, a fullrowalternatepickup and dispersealternatedropping automatic seedling transplanting machine was designed, which was applicable for transplanting from plug trays to plug trays or to flowerpots with high location accuracy. The working process and principle of transplanting machine were introduced. The optimal transplanting strategy was selected and mechanism structure of the whole machine and disperse component for endeffectors was designed based on the fullrowalternatepickup and dispersealternatedropping requirement. To improve location accuracy affected by motion of transplanting platform and synchronous belt flexible deformation, the rigidflexible coupling model of transplanting platform was established and simulated in ADAMS under the transplanting horizontal motion of constant acceleration and deceleration, cubic polynomial and quintic polynomial. The results indicated that the location accuracies under three motions were all higher than 99.7% and the one with quintic polynomial was the highest. The location accuracy experiment of transplanting platform and the whole transplanting performance experiment were conducted under different transplanting efficiencies. The results showed that the designed mechanism was reliable with a success transplanting rate of 90.23% at speed of 120 seedlings/min and the location accuracy was 0.15~1.22mm.