Abstract: For equipment insulation, the temperature between the two layers of the insulation is the maximum allowable operation temperature for the outer layer material, and is subject to the temperature change in both inner and outer layers. Both the inner and outer layers of the insulation materials shall be reasonably adjusted in thickness to obtain an economic two -layer system thickness. According to thermodynamics, the optimal objective function and constaint conditions are established for temperture - constained two lay-t'r insulation, and the constaint optimization is realized using the method of intrinsic penalty function. It is believed that the objective function, constaint conditions and solution for the two layer system are applicable for calculation in actual engineering. An example is given for calculating the economic thickness of the two -layer insulation in the walls of the heaters in a pump station.