The Ag electrodes were fabricated on the p-type gap surface, and the annealing environment was used to make good Ohmic contact at the contact interface between the metal and the semiconductor. The influence of different annealing environments on Ohmic contact surface was also investigated by characterization and comparison of scanning electron microscope (SEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results show that if the annealing time is too short, the area of atoms moving freely with energy is small, which is not conducive to improving the surface denseness of the sample. And if the annealing temperature is too high, the grains on the Ohmic contact surface are easy to merge, causing the roughness of the sample surface to increase. In addition, during the annealing process, the mutual diffusion, the formation of the compound and the alloy phase, and the oxidation reaction will also affect the Ohmic contact surface characteristics. Among them, the oxidation reaction is more intense than other reactions and has a greater effect than the contact resistivity. Therefore, a suitable annealing environment and effective control of the oxidation reaction are key to enhance the Ohmic contact performance.