Abstract: To analyze effect of rotation ratio α and swing ratio β on distribution uniformity of grain trajectory during wafer polishing, two models are established, namely relative velocity between wafer and pad, and grain trajectory on wafer surface.Distribution law of relative velocity and particle trajectory density statistics are studied.Resultsshow that when the rotation speeds of wafer and pad are kept consistent, the relative speed is stable.It is also found that the reciprocating motion of wafer following polishing head mainly influences periodicity of relative speed changes and randomness of grain trajectory distribution.In conclusion, when α=1.01 and β=0.2, the homogeneity of grain trajectory distribution on wafer is the best.