The invention discloses a self-adaption automatic vortex flaw detection method for noise change of a parent metal body. Aiming at workpieces formed by butt-jointed and fixing a plurality of different materials or parts having identical materials while having a plurality of surface processing methods, a vortex detection method is adopted, according to the relative ratio between body vortex noise signal amplitudes of the different materials or parts having different surface processing methods, the automatic change program of the signal gain parameters can be set, and the signal gain parameter or alarming threshold values can be automatically adjusted so as to adapt to the sensitivity requirement of different parent metal blocks and prevent the misjudgment or detection leakage of flaw signals.