The transplanter is the core structure of tobacco transplanting machine The working way applied offset-double disk and four-link rotation, for planting seedlings and floating seedlings. After the characteristic coefficient ?? 1 is the essential condition for designing the transplanter and ensuring the normal operation of the transplanting quality. The values of the design parameters were determined via the orthogonal test in the conditions of the different planting speed and depth to set up the mathematics model of the dock-mouth trajectory.