Abstract: The n-type porous silicon with different morphologies were synthesized by the electrochemical corrosion method.Different kinds of side-wall etching in same directions were observed by SEM in spite of different corrosion conditions.Experimental and theoretical analysis showed that the appropriate intensity of electrical injection holes played a critical role in forming the smooth side-wall.The overdosing holes will form barrier layer in the wall,which promote the minority carrier in the bulk to drift from the side-wall to interface between the side-wall and the electrolyte.