Prior to the design and construction of any fruit harvesting machine it is essential to know the physical and mechanical properties of the trees and of its fruits. An example could be cited as the force needed to overcome. The strength with which the fruit is attached to the stem, in trunk shaker harvesting. In this research the acting forces on the fruit during harvest, including tensile strength, bending moment and torsion strength were assessed and analyzed. Experimental measurements were made on some major varieties of Iran’s walnuts (Kaghazi, Khooshei, Soozani and Badami) at Damavand, Kan and Savojbolagh in the countryside vicinity of Tehran. Data were analyzed using a factorial experiment in the form of a completely randomized block design of 15 replications. Analyses showed that the highest mean values of tensile, torsional and bending strengths belonged to Badami (31.12 N), Soozani (9.54 N.cm) and Kaghazi (50.13 N.cm), respectively, while the lowest mean values of strengths belonged to Khooshei with 21.73 N, 7.41 N.cm and 21.42 N.cm. The results finally indicate that the effects of region and interaction between regions as well as variety on bending strength are significant at 5% level. The effect of variety in different varieties of walnut on tensile strength, bending moment, and torsional strength of walnut fruit was significant at 1% level. Considering the results of the conducted experiment, Kooshei variety needs a minimum of forces for harvesting so it could be concluded that mechanical harvesting of this variety as compared to other varieties is preferred, and thus more strongly recommended.