(Et₂MN₃)_n (n=1 to 3，M=Al，Ga) clusters were studied by DFT/B3LYP method with SDD basis set. The dimer(Et₂MN₃) ₂ and trimer(Et₂MN₃)₃ (M=Al，Ga) are found to exhibit four-membered M₂N₂ and six-membered M₃N₃ ring structure，respectively. Compared with the monomer，the order of the bond length changes for the dimer(Et₂MN₃) ₂ and trimer (Et₂MN₃)₃ (M=Al，Ga) is as follows: N_α—M>N_α—N_β>N_β—N_γ≈M—C. Binding energies of the dimer (Et₂AlN₃) ₂ and trimer(Et₂AlN₃)₃ clusters are 35.44 and 45.61 kJ·mol^-1 lower than that of (Et₂GaN₃) ₂ and(Et₂GaN₃)₃ clusters，respectively. Thermodynamic properties show that the dimer is the main composition of the(Et₂MN₃)_n (n=1 to 3，M=Al，Ga) clusters at 298.2 K. The dimerization and trimerization are very favorable thermodynamically below 500 K.