Taking separated multeity machine as the research object, the three-point hitch linkage for the rototilling-planting combined machine was designed. The design was started with the principle of three-point hitch linkage. The effective clearance of single combined mechanism was analyzed. The capsize resistance was analyzed by the unit’s longitudinal stability coefficient and climbing stability coefficient. The maximum effective distance was 41cm. From analyzing the moving states of rotary blades, the place of clods and the muzzle velocity, the minimum effective distance was 19cm after several times of calculation and experiment.