Abstract: To study the metal-metal interactions and their effects on 31P NMR,the structures of mononuclear complex Fe(CO)3(MePhPpy)2 1,binuclear complexes Fe(CO)3(MePhPpy)2(MCl2)（2:M=Zn，3：M=Cd，4：M=Hg）and Fe(CO)3(MePhPpy)2(HgCl2)2 5 are calculated by density functional theory (DFT) PBE0 method.The following conclusions can be drawn as follows. (1)the stability of complexes is 243. (2)The Fe-M interactions is 234. (3)The Fe-M interactions mainly act as Fe-PnM and Fe-CnM charge-transfer interactions, and the N-M interactions mainly act as nNnM.（4）The calculated 31P chemical shifts in 1,3,5 are consistent to experimental results. Therefore, the DFT-PBE0-GIAO method is employed to predict the 31P chemical shift of 2 and 4 with 61.66ppm and 56.49ppm. (5)The increase of Fe-C*Fe-P delocalization and the decrease of Fe-P*Fe-C interaction raise the electron density of P nucleus in the binuclear complexes，so the 31P chemical shifts of binuclear complexes are smaller than that of mononuclear complex.