Aiming to address the current issues with garlic combined harvesters’ stem-cutting devices, including suboptimal cutting performance, high cutting resistance, delayed cutting causing bulb damage, and clogging of gripping and conveying mechanisms, an SPH-FEM coupled algorithm was employed to design a dual-disc garlic stem-cutting device. Dynamic analysis and parameter optimization were subsequently conducted. Firstly, the material model for garlic stems was established based on their structural characteristics, physical parameters, and mechanical properties. A simulation model of the garlic cutting process was constructed by using ANSYS/LS-DYNA. Finite element simulation results determined the optimal blade disc parameters: disc thickness of 2mm, blade angle of 15°, and blade overlap of 15mm. Single-factor simulation tests were conducted by using the model to establish the operational ranges for the garlic cutting device: feed rate of 1.5~2.5km/h, disc rotational speed of 400~600r/min, and disc spacing of 1~3mm. Finally, a Box-Behnken design, a three-factor, three-level orthogonal combination test plan was implemented. Bench tests determined the maximum cutting resistance of the disc under each factor level. Design-Expert 13 was employed to conduct variance analysis and response surface analysis on the test results, yielding the optimal operating parameters for the garlic stem-cutting device: feed rate of 2.1km/h, disc rotational speed of 560r/min, and disc spacing of 1mm. Bench test results indicated that under optimal operating parameters, the maximum cutting resistance was 7.33N with an error margin of 7.5%. This dual-disc cutting device exhibited low cutting resistance, stable performance, and produced relatively flat stem cross-sections. Crucially, no bulb damage occurred during testing, fulfilling the stem-cutting requirements for garlic harvesting. It provided valuable reference for designing combined garlic harvesting machinery.