A power electronic system fault detection method and apparatus are provided. The method comprises steps of: acquiring an electric signal on the converter side of a power electronic system; decomposing the electric signal at least once to obtain a decomposed signal; determining whether a modulus maximum value exists in the decomposed signal; extracting the characteristic value energy signal of the electric signal if so; and determining the fault condition of the power electronic system according to the characteristic value energy signal. Thus, the method determines whether the power electronic system has a fault accurately in real time.