An abnormal regulation of the stagger angle deteriorates the internal flow field and pressure pulsation, leading to an augmentation of aero-acoustic noise and vibrations in variable-pitch axial fans. To evaluate the effects of an abnormal stagger angle, the pressure pulsation and transient flow field under normal and abnormal regulations of the stagger angle were simulated using unsteady 3D modelling. The characterization capabilities of the approximate entropy and sample entropy for identifying an abnormal deviation were examined by extracting the features from the static pressure signals. The results indicate that, after an abnormal deviation of stagger angle, the periodic and quasi-periodic pulsation distributions of the static pressure are distinctly hindered, and the impacts of an abnormal deviation angle on the pressure distributions in the time and frequency domains are intensified with increasing deviation degree, resulting in increased pressure fluctuation intensity. The transient flow field clearly changes with time and degree of deviation, and abnormal high- and low-pressure regions are developed. Both the approximate entropy and sample entropy can be used to identify an abnormal blade deviation, but the sample entropy is more suitable for characterizing the effects of deviation degree on the static pressure at the impeller and guide vane outlets. (C) 2017 Elsevier Ltd. All rights reserved.