A Zhen’an Temple iron bull has serious corrosion problems; furthermore, the mechanism of corrosion is complex. We tried to clarify the type of corrosion products of the iron bull and the factors influencing the corrosion, in order to provide a basis for its subsequent restoration and conservation. Scanning electron microscopy (SEM), X-ray diffractometry (XRD) and laser confocal Raman spectrometry were used to analyze the phase composition and rust layer structure of the surface corrosion products of the iron bull thus to understand the mechanism of corrosion. The results show that 1) the belly of the iron bull is hypoeutectic white cast iron, and the iron bull structure contains various phases and inclusions, which reduces its corrosion resistance; 2) the surface corrosion products of the iron bull exhibit serious delamination; the outer and inner corrosion products are dense, with the main components being goethite and Fe₃O₄; 3) the corrosion products in the middle layer are relatively loose, the main components of which are lepidocrocite and hematite; 4) the corrosion products of the ear, left foot and tail of the iron bull mainly contain goethite, lepidocrocite, Fe₃O₄ and hematite, etc.; goethite has the highest content in the rust products; 5) there are obvious differences in the compositions of the corrosion products of different parts of the iron bull—the ratio of goethite to lepidocrocite of the corrosion products of the ear is the smallest while that of the left foot is the largest. The factors influencing the corrosion and mechanism of corrosion of the iron bull were then analyzed.