The present disclosure discloses a nonlinear sparsity-based instantaneous dynamic frequency fault diagnosis method for an aviation intermediate bearing. In the method, a vibration signal and a rotating speed signal of high and low voltages of the intermediate bearing are acquired, and a vibration signal fragment x under a specific working condition is intercepted according to the rotating speed signal; a nonlinear sparse time-frequency enhancement model or a nonlinear sparse enhancement algorithm model is established based on derivative window function short-time Fourier transform of the vibration signal; the nonlinear sparse time-frequency enhancement model is solved or the nonlinear sparse enhancement algorithm model is improved by using a fast iterative shrinkage threshold algorithm and combining a k sparse strategy, and finally a nonlinear sparse time-frequency representation result {circumflex over (N)}x, may be obtained through iterative optimization.