In the Chinese ancient times around 200 B.C., bronze arrow was a kind of weapons in mass manufacturing and one - off use. Comparing to the strict demanded bronze sward and ritual vessel - Ding, the low performance bronze arrows exhibited a great difference in material selection and surface treatment. Therefore, the rust - eaten process of the arrows will really represent a variation of the materials after several thousand years, especially, in the complicated environments in the middle Yangtse River region. This paper studies the rust–eaten phenomenon and mechanism of the bronze arrows made in late Spring-Autumn age by using scanning electron microscopic (SEM), energy–disperse spectrometer (EDS), X-ray diffraction (XRD) and microhardness tester. It was found that the microstructures of bronze arrows were composed of three distinctive layers including a completely mineralized layer, transition layer and core original material. Different layers exhibited different microstructures, chemical compositions, compatibility and microhardness. The formation mechanism of the micro-cracks in the cross-section rust - eaten layer was firstly observed and analyzed, i.e., the crack paralleling to the surface was caused due to expanse disbonding in the mineralized layer which would further develop into a rust powder , while the radial crack perpendicular to the surface was due to the arrow rod expansion in the poor ductility mineralized layer. It is considered that the rust-eaten process of bronze is the result of impurity diffusion gradually along the grain boundaries between [alpha] solid solution and [alpha] + [delta] eutectoid grains, cavities and other defects where possess higher boundary energy in atmospheric environment.