Based on constructal theory，the “volume-point” heat conduction constructal optimization with triangular element at micro and nanoscales is carried out by taking minimum dimensionless maximum thermal resistance as optimization objective and releasing the constraint that the new-order assembly should be assembled by the optimized last-order assembly.The optimal construct of the “volume-point” heat conduction model under the effect of size effect is obtained.The results show that the optimal constructs with size effect and without size effect are obviously different.The heat transfer performance of the new-order assembly obtained by last-order assembly optimization constructal design method is not always the optimal one；compared with the global optimization constructal design method with the last-order assembly optimization constructal design method，the temperature limitation of the triangular assembly can be effectively reduced by using the global optimization constructal design method，and its heat transfer performance can be obviously improved.