Optimal design for sourcing, grading and other post-harvest operations requires the availability of appropriate information about their physical properties. Also, achieving a high quality product requires the fight against weeds and impurities in the product. Therefore, in this research, some physical properties of wheat and barley were measured. A gravity separator was also used to separate the barley in the wheat mass. This machine has five customizable parameters includes air velocity, frequency of oscillation, amplitude of oscillation, longitudinal slope and latitudinal slope of the table. The effect of these parameters was investigated in the form of two factorial experiments in a completely randomized design to achieve maximum separation of barley from wheat mass. The results of experiments showed that in the conditions of air velocity of ?.?? m / s, the oscillation amplitudes of ? mm, the longitudinal slope of ?.? degree, the latitudinal slope ?.?? degree and the frequency of oscillation of ??? cycl / min, the maximum separation of barley from wheat mass to ??.? % was achieved. In most cases, with increasing latitudinal slope from ?.?? degree to ?.?? degree , the longitudinal slope of the table from ?.? degree to ?.? degree and with the increase of the frequency up to ??? cycl / min, the separation of barley from the mass of wheat decreases. Also, the minimum amount of barley separation from wheat mass in condition of oscillation frequency of ??? cycl / min, l o n g i t u d i n a l slope of ?.? degree, l a t i t u d i n a l slope of ?.? degree, oscillation a m p l i t u d e of ? mm and air v e l o c i t y of ? m / s was o b t a i n e d ?.??? %.