Abstract: Abnormal conditions to the first stage rotor blade of a compressor were found when magnetic powders inspecting after polished, and then macrostructure examination to the abnormal position was performed. It is found that there were multiple-lines defects similar to cracks on the convex airfoil surface of the blade along with longitudinal direction, and then means of metallographic examination and energy spectrum analysis were employed to investigate the formation reasons of the defects. The results indicate that the defects of the blade were induced by the slags carried from the smelting process of the raw material, and the slags were crushed during the following pressure deformation process and distributed in banded shape along the longitudinal direction at local of the blade.