BACKGROUND: In the process of tillage, flat knives of rotary cultivators are to carry out the process of cutting soil and weeds with minimal energy consumption and not to become clogged with weeds, which is due to the compliance of the parameters of their blades with operating conditions. However, despite the abundance of works devoted to the study of the working process of flat knives of rotary cultivators, there is not any method of a comparative assessment of the various shapes of their blades. AIM: Development of the method for comparing different blade shapes of flat knives of rotary cultivators. METHODS: The research design included studying the following issues: clarifying the conditions for weeds to fall off the curved blade of a flat knife performing a plane-parallel movement; determining the equation of the curve of a knife blade that satisfies the condition of weeds to fall off the blade; development of methods for comparative analysis of the energy intensity of the process of cutting soil with flat knives with blades of various shapes; experimental verification of theoretical conceptions. The study objects were the processes of interaction of weeds and soil with the blades of flat knives of various shapes. The studies were conducted during 2022 and 2023. RESULTS: The condition for weeds to fall off the curved blade of a flat knife performing a plane-parallel movement has been clarified (a more informative form of notation), based on which an equation for the rational curve of the blade has been obtained. The comprehensive method has been developed for comparing different shapes of blades of flat knives of rotary cultivators, according to the criteria of compliance with the condition of weeds to fall off the blade and the energy intensity of soil cutting. Examples of the application of the method for the analysis of various shapes of blades of flat knives of rotary cultivators and the development of one of the effective shapes, as well as the results of experimental studies are given. CONCLUSION: The proposed method helps to give specific practical recommendations on the advisability of using knives of one shape or another in the operating conditions under consideration, taking into account the operating parameters of the machines, as well as to create effective combined blades.