Aiming at the problem that fracture of blade exists in the aeroengine compressor, this paper proposes a testing methodology by using composite bending-torsional resonance of the square plate testing specimen, and researches on nonlinearity vibration characteristic and vibration fatigue testing method of the specimen. The results show that simulated testing specimens have quite complicated nonlinearity characteristics of softening and hardening to seriously impact on vibration fatigue testing of the specimen. And the phenomenon of amplitude jumping is obvious because of nonlinearity, driving frequency must be slightly less than peak frequency to maintain vibration stability. In order to accurately determine testing specimen crack appearing node, crack criterion is developed. Fatigue strength can be accurately determined by the developed crack criterion, and the test and the verification show that the crack criterion is valid and feasible.