A method for determining snakelike instability of a rail vehicle includes noise-assisted ensemble empirical mode decomposition (EEMD), instantaneous frequency (and amplitude ), generalized zero-crossing (GZC) frequency (and amplitude ), and non-linear index calculating methods. If snakelike instability occurs to a train, the non-linear index of the train is enhanced, so that early warning can be given for possible instability. The invention provides a novel method for determining snakelike instability. The method includes calculating instantaneous frequency, instantaneous amplitude, zero-crossing average frequency (amplitude) and non-linear index, and determining the snakelike instability according to the non-linear index. The defect of unreliable determination of a conventional determining method is solved.