The contact characteristics of Au/ p-InP in hetero-junction InP/InGaAs detector were studied in this work. Under the annealing condition of 480℃ for 30s, the ohmic contact was formed with the room-temperature special contact resistance 3.84×10-4Ω·cm2. Temperature-dependent characteristics of ohmic contact were investigated. The results indicate that the special contact resistance increases with decreasing temperature, the current transmission mechanism at the interface is thermion-field emission mechanism (TFE) at the temperature of 243 K to 353 K; while below 240 K, the contact performance presents schottky property. By means of scanning electron microscope (SEM) and X-ray diffractometer, the diffusion degree and metallurgical reaction at the Au/InP interface were investigated，and the penetration degree is very heavy at the interface of sample after annealed at 480℃for 30s and the generation of Au10In3 produced by metallurgical reaction contributes to improve the contact performance of Au/p-InP.