Abstract: ICP etching technology was used to etching GaAs material which was coated with photoresist of different thicknesses and the slope angle of different patterns was studied.The dimensional effect of the GaAs material with small graphics in the etching process was discussed,the size gain and particle scattering model was also proposed to explain the fact that the slope angle of GaAs material coated with large photopersist thickness varies apparently.On the basis of the above research on the influence of the photopersist thickness to the slope angle,the influence of different etching selectivity was also studied.The fact was explained on two aspects,which contains GaAs dry etching mechanism and the effect of ICP etching parameters to the physical and chemical processes.