Powdery corrosion is called as cancer of cultural relics of bronze. For many years the experts concerned at home and abroad can not make distinct progress in the control or cure of powdery corrosion. This paper introduces in detail analyses of XRD, SEM, TEM and XRFA on an Ancient Bell fragment with serious powdery corrosion from Cai Hou Tomb, points out that the components of powdery corrosion are mainly atacamite Cu₂(OH)₃Cl, cuprite Cu_2o and cassiterite SnO₂ with worse crystalline state. In Ancient Bell matrix, there are corrosion gullies which phase components are consistent to powdery corrosion. Obviously, this discovery has very important significance to study the formation mechanism of powdery corrosion.