Abstract: Some unusual sounds appeared when an aero-engine was servicing. When it was checked on the ground it was found that all the HP1, HP2 turbine blades and HP2 guide vanes fractured. By means of on-site investigation, fracture analysis and metallographic examination, it was found that the HP1 turbine blade which fractured at the root elongation was the first fracture part, and the gathered distribution of casting loose defect was the main cause for the early fatigue fracture of the HP1 turbine blade. Fracture of all the other turbine blades was overload fracture caused by secondary injury.