Abstract: The rupture of the Al-Ni-Co magnet steels used aero-engine rotor is investigated with comprehensive analysis.Metallurgical quality analysis of Al-Ni-Co magnet steel shows that the quality of this steel under vacuum casting is better than that steel under atomosphere casting.The reliability n use for the former is secure. A lot of insclusion, such as Al2O3,TiN,i TiS, etc, ar.e formed resulting in the rupture of the alloy at work.