At present, the all-filming double-furrow technology has been spread in large areas in Gansu province, but the majority of the hill-drop equipments applying in this technology exist problems of picking or tearing films, high labor intensity and low production efficiency.In view of the above problems, put forward a kind of hill-drop planter which used the nearly constant speed unit.The planters working principle was that the crank connecting rod mechanism and the nearly constant speed unit control to penetrate and unearthed soil action of the hold former.When the hold former of the crank connecting rod mechanism penetrate and unearthed soil, the nearly constant speed unit provides nearly constant velocity which relative to the frame,the velocitys direction and the tractor opposite, but their size are approximately equal, so as to ensure the hold formers speed in the horizontal direction which relative to the ground is approximately zero, and the hold former penetrate and unearthed soil verticality.By theoretically analyzing the nearly constant speed units motion, determined the factors that influence the nearly constant speed, used Adams/View to optimized the design parameters of the nearly constant speed unit, and the optimal solution was obtained.Simplified the whole 3D model, used the SolidWorks Motion to conduct motion simulation, get the movement track of hold former, and it is consistent with the theoretical calculation.This study provided a reference for the design of film hold former.