Blade cracks pose a serious threat to aviation safety and lead to serious aviation accidents. In order to diagnose cracks at the early stage, the nonlinear vibration of cracked blades was investigated theoretically and experimentally. A nonlinear dynamic model was established to link the crack size and the dynamic parameters. A coupling quantification expression of the coupling component power in the nonlinear vibration response was obtained. This response expression indicated that the harmonic element power was determined by the adjacent component power, component order, and positively correlated with the depth of the blade crack. Therefore, based on the relative power of the vibrational components, a crack detection method is proposed. Results of the simulation and the testbed experiment both show that the cracked blades are effectively separated from the normal blades by this method.