Abstract: Manufacturing burnish-mark (MBM) caused by the slight polishing on the out surface of the steam generator tubes during manufacturing process is to affect the eddy current signal.It is discovered during eddy current test that MBM related signal amplitude is affected by different configurations of the eddy current instruments.This paper mainly studies the influence factors of MBM signal amplitude based on experiments and theoretical analysis,and it also aims to find out the corresponding relationship and proposes the method for eliminating these factors.