Aimed at the vibration signal feature of the coupling misalignment fault during operation of centrifugal fan，the empirical mode decomposition method is used to analyze the effect of the load and the speed change on misalignment fault fre quency and its peak. Intrinsic mode functions containing specific frequency can be obtained from the decomposed fault signals. To eliminate the noise influence on the AR model, the 3σ criterion by hard valve value is used to depress noise included in every IMF，and then its AR model is established for the spe ctrum analysis. It is indicated that the second harmonic peak is the dominating compo nent, besides the base frequency, and the third-harmonic peak changes signi ficantly while the load and the rotational speed rise, and the vibration caused by mis alignment is aggravating.