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Mainstream fruit and vegetable harvesting end-effectors differ greatly in structure according to the varieties of fruits and vegetables harvested and the wood fiber materials of fruit stems, and all of them have the problems of large space occupation, heavy structure, easy collision with fruits and easy damage, which is not conducive to cutting fruit stems. Therefore, it is very important to study an ultrasonic cutting knife with flexible structure, small space occupation and labor saving for cutting different wood fibers of fruit and vegetable harvesting end-effectors. The theory-finite element-experiment method was used to analyze the mechanism of cutting fruit stalks with ultrasonic cutter. Firstly, the physical field model of cutting fruit stalks by ultrasonic tool was established. Through the time-space analysis of the cutting process, the mathematical models of displacement, speed and acceleration were established, and the time-space discontinuity of the cutting process was analyzed. Based on the fracture mechanics, the cutting mechanism of fruit stalks was studied and the Matlab response surface diagram was drawn. It can be found that the force required for ultrasonic cutting was less than that for conventional cutting. Using finite element analysis software, the modal analysis and harmonic response analysis of ultrasonic tool were carried out, and the vibration modes of the tool at different frequencies and the optimal frequency for cutting were obtained. Finally, the ultrasonic cutting experiments of tangrine and orange stalks with different diameters were carried out by using a selfmade test bench at different cutting speeds. The experimental results showed that the cutting speed and vibration frequency were related to the cutting force. Under the high-frequency and low-frequency vibration, with the increase of fruit stem diameter, the cutting time was changed within 0.4s, and the cutting efficiency was stable. In the experiment, the maximum cutting force of ultrasonic cuttingwas much less than that of conventional cutting, which was less than 1N. Ultrasonic cutting can effectively reduce the cutting force and reduce the impact during cutting. Compared with conventional cutting, ultrasonic cutting had stronger cutting ability, and it was suitable to be applied to the end-effector of harvesting, thus achieving higher recovery efficiency.