The mineral composition, corrosion layer structure and the metallography of some typical ancient bronze samples with or without powdery rust were analyzed and compared by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive analysis (EDS) and optical microscope (OM). It was discovered that the corrosion layer of bronze without powdery rust could be divided into two layers, the outer was cupric oxides in which metallograph tissue the [alpha] + ([alpha]+[delta]) components had not been found and the hydroxyl cupric chloride had not been detected in the rust, and the inner was cuprous oxide. However, in the ancient bronze's powdery rust, the presence of hydroxyl cupric chlorides had been found, and cross section of the corrosion rust could be divided into three or four layers having structures and elements composition different from each other. In the layer of powdery rust immediately neighboring with the matrix of bronze, a large amount of cuprous chloride had been detected. The results have demonstrated that the fundamental factors on the formation and development of bronze powder rust were the compactness of the surface rust covers, air humidness and the presence of cuprous chloride layer near the matrix of bronze artifacts.