Abstract: The design of the cutting device of a walk-type pasture reaper was improved to solve the problems existing in using mono-acting cutter, such as the poor balance, the low cutting speed, the easily to be blocked, the difficulty to cope with the soft forage. The improved design applied the double-acting cutter device, whose double-acting cutter cut reversely each other driven by a double-camshaft linkage. Based on the kinematic analysis of the cutting device, this paper calculated separately the relationships of the angle of crank with the displacement, the velocity and the acceleration of knifes, and performed optimal design of the structural parameters of blades and the cutting clearance. By analysis of the cutting speed ratio, this paper also drew the cutting graphs of the double-acting cutter under different cutting speeds ratios. And it showed that in order to reduce the repeated cutting area and the fail to cut area, the optimum cutting speed ratio (K) is 1.6. The research provided references for the further optimal design and experiment of the cutting device of the walk-type pasture reaper.