Abstract: Sugarcane, as an important cash crop in China, produces a large number of sugarcane leaves after harvesting.At present, the cane leaf crushing and returning machine used in china is easy to damage the old roots and reduce the germination rate.Therefore, the cane farmers generally burn on the spot and pollute the environment.Based on sugarcane leaf shattering counters-field set at the same time does not hurt perennial root as the research background, the core components of the sugarcane leaf shattering counters-field knife shaft assembly is studied, based on three dimensional mathematical model established, from the knife shaft speed calculation, dynamic balance check, line density and the way of determination, allowable residual unbalance to the tolerance analysis and the distribution of the plane, introduced the knife shaft assembly design and analysis method.The results provide reference for the reliability improvement of sugarcane leaf crushing and returning machine.