Abstract: Effects of oxidizer hydrogen peroxide(H₂O₂)and complexing agent chitosan oligosaccharide(COS)on material removal of aluminium alloy were investigated in alkaline slurry by using atomic force microscope(AFM), X-ray photoelectron spectroscopy(XPS)and nanoindentation tests.In addition, the chemical effect of H₂O₂ and COS occurred in CMP process was discussed.The results show that the material removal rate increased as the COS concentration increased when the mass concentration of H₂O₂ was 2%.It can obtain remarkably smooth surface R_a=2.5 nm and 861 nm/min removal rate when the mass concentration of COS reached 0.32%.The material removal rate was enhanced by the increase of H₂O₂ concentration when the mass concentration of COS was 0.5%.After reaching the maximum value, the material removal rate began to decrease.The surface roughness was 3.52 nm and the material removal rate was 840 nm/min when the mass concentration of H₂O₂ reached 1.2%.A weak passive layer is mainly consisted by Al-COS、Al₂O₃ and Al(OH)₃ when COS was added.