The electromechanical coupling coefficient (K₃₃) is a crucial parameter to express the efficiency of the magnetostrictive alloy. Fe_72.5Ga_27.5 magnetostrictive oriented crystal has been prepared by zone melting unidirectional solidification. The K₃₃ values of the directionally solidified sample and its quenched sample(1000℃/3 h, W. Q.) were determined by improved AC impedance resonance frequency testing method. The DC magnetic field was formed by the DC coil and the pre-pressure was given by the press-pack. Since the magnetostriction of Fe–Ga Alloy is less than that of the giant magnetostrictive material of Tb–Dy–Fe by 10 times, the K₃₃ of Fe–Ga alloy cannot be determined by the traditional testing methods. In this paper, a 4–wire configuration connection was used to pickup the signal in experiment, and the AC excitation signal was adjusted to 0.5 A, so that the obvious and stable AC impedance curves of the Fe–Ga alloy were acquired. When the DC magnetic field is 32.7 mT and no compressive pre–stress is applied, the K₃₃ values of the directionally solidified sample and quenched sample are 0.103 and 0.137, respectively. The K₃₃ values of the two kinds of Fe_72.5Ga_27.5 magnetostrictive alloys decrease with increasing DC magnetic field, and increase at first then decrease with increasing pre–pressure, but the K33 value of the quenched sample always higher than that of the oriented sample.