Abstract: Present situations were made on structure of flail knives in crushing device for forest slash and analysis were carried out on principle ofimpact crashing of knife. Based on Solidworks, 3D model of flail knife was established to study static analysis in ANSYS environment. And flailknives were designed with structural parameters as variables, the minimum safety coefficient and quality as multi-goals for optimization. A new 3Dmodel was built with the knife bole diameter of 10.862 mm and knife thickness of 11.032mm, without changing the other parameters. Model forbonded-crushing of forest residue was established by EDEM. Orthogonal simulation tests were implemented by importing the model of flail knifebefore and after optimization into EDEM. The result demonstrated that it had more number of bond breakages, indicating better crushing effect.