Objective To research the deflection of the whisker in the plasma sprayed alumina coatings, thus provide new ideas to enhance the erosion resistance. Methods The flattening of plasma sprayed droplets was simulated by FLUENT software after the droplets impacted on a flat substrate. And the deflection of whisker was characterized using ANSYS software during the flattening process of droplets. Results The flattening of droplets was observed after the impact which lasted about 1. 5 μs. When the moment shifted in the range of 1×10 -18 to 3×10 -18 N·m, the maximum deflection angle was increased from 23° to 70°. Conclusion The finish-time of flattening is obtained by studying the effect of impacting duration on the droplet shape and maximum flattening velocity. The flattening velocity of droplet flow along the substrate surface is affected by the impact velocity. Deflection of whisker occurs when the moment is changed in certain range.