Mechanized harvesting of oil tree peony fruit is an important condition for the industrialization of oil peony. It is of great significance to improve the self-sufficiency of edible oil and solve the contradiction between supply and demand of edible oil. However, the existing oil tree peony fruit harverster can only partly meet the needs of mechanized operation, but the cutting mechanism of the stem and cutting tool parameters is still lack of sufficient theoretical research, and the optimal design of the fruit harvester has not been realized. Therefore, this paper considered the oil tree peony stem as the research object, and carries out experimental research on the macro cutting mechanism, microstructure difference and shear deformation characteristics of the stem. Based on this, a stem cutting constitutive equation is established, and the key parameters of the cutting tool are optimized through the finite element simulation method, which provides a theoretical basis and technical support for the design of oil tree peony fruit harvester.