As Weigert effct is studied, the dichroism of W sheet can be enhanced in which the guide temperture is raised. If the prefabricated plate is preheated previously,the dichroism will be weakened (this result is defined as abnormal heat effect).In this paper, We clarify the physical appearance and the experimental law of the abnormal heat effect among the preheating time and the guide temperature, and give it a inital explanation for micromechanism.