Abstract: The basic rule of metal magnetic memory(MMM) technique is that under the influence of stress,there will be magnetic leakage field on the surface of ferromagnetic materials in stress concentration(SC) and distortion zones.It is possible to determine SC zones according to measuring changes of normal component of magnetic leakage field.By applying MMM and ultrasonic to fourteen jointing armor plats,the validity of MMM technique is validated and a lot of availability experience is achieved.