The use of circulating fluidized bed as common failure cap model, in cold bubbling fluidized bed test rig of fluidized bed under normal condition and fault cowl conditions include the operation condition of the complex multiphase flow inside the chamber of a stove or furnace is simulated. Lee on normal cowl and fault cowl conditions indoor pressure fluctuation signal acquisition, application Welch power spectrum estimation method and treatment of pressure fluctuation signals collection, it is concluded that two kinds of working condition of the power spectral density (power spectral density, PSD) distribution. Compared to normal cowl and fault cowl fluidized bed under the condition of indoor wind power spectral density distribution of pressure fluctuation signal to extract the fault characteristic value, to realize the circulating fluidized bed cowl fault detection and diagnosis. Experiment shows that this method can fault detection and diagnosis of fluidized bed hood. Put forward the application of fluidized bed hood Welch power spectrum estimation method fault detection method, for on-line detection of fluidized bed hood malfunction to provide the reference value.