In order to aid in engineering design and modification of cutting mechanisms in soybean harvesters and to investigate the effects of parameters on cutting energy, an impact shear test apparatus was designed and constructed to measure the energy required for cutting soybean plant stems. Experiments were carried out on Iranian Sahar variety, in different blade velocities (2.5, 3.75, 4.5 and 5.45 m s(-1)) to determine the optimum values of blade bevel angles (18, 23, 28, 33 and 38 degrees), oblique angles (10, 20, 30, 40 and 50 degrees) and tilt angles (15, 25, 35, 45 and 55 degrees). The results show that the optimum value of Specific Cutting Energy (SCE) was obtained at blade bevel angle of 23 degrees, oblique angle of 30 degrees and tilt angle of 25 degrees and blade velocity of 3.75 m s(-1).