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Tb0.3Dy0.7Fe1.90 oriented rods were prepared by zone melting with unidirectional solidification. The magnetomechanical coupling factor (k33) was measured by magnetomechanical resonance under different DC bias fields up to 77.4 mT. An effective method was provided to calculate sonic velocity, elastic modulus and compliance constant through measuring resonate frequency (fr), and calculate dynamic magnetostriction(d33) via measuring magnetic permeability, magnetomechanical coupling factor(k33) and compliance constant. Without pre-stress, resonate frequency (fr), sonic velocity and elastic modulus first decreased and then rose with increasing bias magnetic field. Under 10 MPa pre-stress, resonate frequency (fr), sonic velocity and elastic modulus decreased linearly with increasing bias fields. d33 exhibited the same variation trend before and after heat treatment, but heat treatment weakened the decrease of d33 in low field range.