A series of heat-treatment experiments of zircons from Changle in Shandong Province were conducted at different temperatures in oxidizing and reducing atmosphere. The colors and their variations were studied by UV-NIR spectrometer. The formation mechanism of the zircon colors was discussed on the basis of the experiments. It is found that the color of the zircons after heat-treatment changed into colorless, yellow or orange in oxidizing atmosphere and colorless in reducing atmosphere. All the samples began to fade significantly at 400℃. The results also show that the red and redish brown colors of zircons are attributed to the color center and Fe³⁺ is responsible for the yellow coloration of zircons. Only a low temperature can make zircon change into perfect colorless, and hence the color enhancement of zircon has tremendous commercial value.