The structure of transition state is very significant to further understand the related reaction system auxiliary N–N bond cleavage process. Here, in order to sort out some DFT functionals in searching the transition states in a N–N bond cleavage reaction mediated by the diiron complexes, compare the 45 density functionals with benchmark data of MP2 and DLPNO-CCSD(T) methods. By analyzing the structures and relative energies, we have found that four HGGA functionals (B1B95, mPW1PBE, HSE1PBE, HSEh1PBE) are the more consistently reliable methods. And the B1B95 functionals provide the most reliable energetic properties within 3 kcal/mol of the data of DLPNO-CCSD(T) method.