The effect of the orientation on the magnetostrietion in Fe81Ga19 alloy has been investigated experimentally and theoretically. The Fe81Ga19[001]and[110]oriented crystals were prepared and the magnetostriction was measured under different pre-stress. The saturation magnetostriction of the[001]oriented crystal increases from 170x10-6 to 330x 10-6 under the pre-stress from O to 50 Mpa. The[110]oriented crystal has a saturation magnetostriction from 20x10-6 to 140x10-6 with the compressive pre-stress from O to 40 Mpa. The magnetostriction of[001]and[110]oriented crystals has been simulated based on the phenomenological theory. The domain rotation path has been determined and the resultant magnetostrietion calculated under different pre-stress. The experimental and simulated results both show that the[001]oriented crystal exhibits better magnetostriction than[110]oriented crystal. The enhancement of the saturation magnetostriction by the compressive pre-stress in the[110]oriented crystal is higher than that in the[001]oriented crystal.