Abstract: The magnetostrictive curve of different material steel pipes was determined by experiments, the relation between the amplitude of the ultrasonic waves and the excitation current of the electro-magnetic field in electromagnetic acoustic transducer(EMAT) testing the defects in different material steel pipe was identified by experiments, the optical excitation current was determined, and the vary rule was resembled with vary trendent of pipes magnetostrictive curve .The provided basis for EMAT products design and explorement.