In this paper, Ni/Au/Ge/Ni/Au laminated metals were deposited on the n-(Al_0.27Ga_0.73)_0.5In_0.5P by electron beam evaporation, the ohmic contact with low contact resistance was successfully prepared by optimized annealing process. The specific contact resistance reached 1.4 × 10^–4 Ω·cm² when annealed at 445 ℃ for 600 s. The result of the secondary ion mass spectrometer shows that the solid-state reaction takes place at the interface between the laminated metal Ni/Au/Ge/Ni/Au and n-AlGaInP, then the germanium atoms and indium atoms diffuse outwards due to thermal decomposition and leave vacancies in the lattice. In this paper, the reason for the formation of ohmic contact is attributed to the fact that the germanium vacancy and indium vacancy are occupied by gallium atoms as donors to increasing the N-type doping concentration. The optimized annealing process can improve the ohmic contact performance of n-(Al_0.27Ga_0.73)_0.5In_0.5P with low doping concentration, but the specific contact resistivity has no obvious relationship with the annealing process when the of doping concentration of n-(Al_0.27Ga_0.73)_0.5In_0.5P increased. The Schottky barrier is high at low doping concentration of n-(Al_0.27Ga_0.73)_0.5In_0.5P. So inter diffusion in the annealing process could significantly increase the doping concentration of n-(Al_0.27Ga_0.73)_0.5In_0.5P and reduce the Schottky barrier height. Nevertheless, the Schottky barrier of the sample with high doping concentration is low enough what is not sensitive with inter diffusion. It provides a new method for the preparation of N-electrode of AlGaInP thin film light-emitting-diodes chip, as so as avoid the problem of n⁺-GaAs absorption in the conventional N-electrode preparation method and the problem of electrode dropping. However, there are still some shortcomings in this paper. The disadvantage is that the high doping concentration of n-AlGaInP will affect the crystal quality, which will reduce the luminous efficiency of LED. Therefore, in order to prepare ohmic contact with excellent properties on n-AlGaInP with lower doping concentration, optimizing the electrode design and the surface treatment of semiconductor materials are the keys to follow-up research.