Abstract: A lot of cracked failures of fir-tree serration accurred in the second stage turbine disc of a large numbers of certain types aeroengines in service.The characte of these cracks belongs to mechanical fatigue.In order to find out the cause for the cracked failure,the vibrating stresses of the second stage turbine blades on test bench and their vibrating strains in flight tests have been measured in the conditions of high temperature and high rotational speed.The measured data indicate that several resonance zones really exist in the second stage turbine blades of type A and B engines.Some methods for elimination of the cracked failures of fir-tree serration in the turbine disc are provided.According to the experiece in service,a modification of type B engine hase eliminated the cracked failures of fir-tree serration of turbine disc in its service life.