Abstract Based on Reynolds averaged Navier-Stokes (RANS) equation and Realizable k-e turbulence model, the influence of abnormal deflection of two adjacent moving blades in an axial fan was discussed numerically. The flow field in the rotor, static and dynamic characteristics of normal blades and four abnormal blades combinations under rotating stall are compared. The results show that the abnormal blades have no effect on the number of stall cells. Compared with the normal blades, in the case of non-stall or stall conditions, the positive deflection blades will increase the surface stress of the blade, and the negative deflection blades can reduce it; deformation distribution also has the same law. The deformation distribution of blades is affected by both aerodynamic and centrifugal loading. However, the stress distribution of the blades is mainly affected by centrifugal loading. By modal analysis, the total deformation distribution of the first to fourth-order vibration modes are obtained. The first to third-order vibration modes show the coupling vibration between the blades and hub, and the fourth order is the blade vibration alone.