Abstract: Cutting mechanism of existing forage grass root-cutting machine mostly use slave mode mechanism driving root-cutting knife working.It′s shortcomings are large grassland cutting seam，large-scale loose range and higher disturbance.Innovative design was made for cutting mechanism of forage grass root-cutting machine.Hydraulic cylinder driven parallel four bar mechanism was used to realize sawing of root cutter knife.Stability of root cutter knife was achieved by reciprocating amplitude of cutting mechanism.Motion of parallel four bar mechanism was analyzed according to design and calculation of comprehensive analytical method for mechanical and hydraulic.Mechanism model was built.Expected movement requirements of root-cutting mechanism were realized by emulating.