In this article we investigate the problem of shape optimization of the cooling cavity of the plunger used in the forming process in the glass industry. The paper deals with finding the algorithm for optimization of the shape of inner canal of plunger in such a way, that its outward surface, which realizes cooling of moulded piece, is attained constant set temperature. The results of the numerical optimization to three required target temperatures 700, 750 and 800 degrees C of the surface Gamma(1) together with the distribution of temperatures on the interface Gamma(1) between the body and the heat source before and after the optimization process are presented.