Model of a heat transfer process in heat exchanger with heat leakage is established in this paper. Both the heat flux between the hot and cold fluids and the heat leakage between the cold fluid and outside environment are assumed to obey Newtonian heat transfer law. On condition that the net amount of heat transferred by the cold fluid is given, the optimal temperature configurations of the hot and cold fluids for the minimum entransy dissipation of the heat transfer process are derived by using the optimal control theory. Optimal paths are also compared with the conventional strategies of heat transfer under constant hot fluid temperature and constant heat flux rate operation. The results obtained in this paper could provide some theoretical guidelines for the optimal design and operation of real heat exchangers.