The influence of copper precipitation on the formation of denuded zone (DZ) in Czochralski silicon has been systematically investigated by means of optical microscopy. It was found that, for conventional furnace high-low-high annealing, the copper precipitates colonies generated along the whole crosssection in the specimens contaminated by copper impurity at the first step of the heat treatment, thus no DZ generated. While in other specimens, DZ formed. Additionally, it was found that the contamination temperature can influence significantly the thermodynamics and kinetic process of the formation of copper precipitates. The phenomena also occurred in the specimens underwent rapid thermal-low-high annealing. On the basis of the step by step investigation, it was revealed that the copper precipitates temperature and point defects type can influence the formation of DZ to a great extent.