Abstract: In order to know the feasibility of metal magnetic memory method to test the embeded defect, a long and narrow groove made from the HP345based cylinder body inner wall was studied, the change of self magnetic leakage field normal component curves were analyzed with loads, the method to distinguish the true defect signal from the false one was proposed, the minimum load when the distinguishable abrupt defect signal appeared at the defect was found out, the curves of the abrupt defect signals peaktopeak values and the maximum gradients with loads were classified into 3 stages, and contrast testing thought was proposed for the newlybuilt cylinder.