The Ag electrodes are fabricated on the p-type gap surface, and the annealing environment is used to make good ohmic contact at the contact interface between the metal and the semiconductor. The influence of different annealing environment on Ohmic contact surface is studied (SEM) and comparison of scanning electron microscope (AES) and characterization of x-ray photoelectron spectrum (XPS). The results show that the annealing time is too short, the energy is small, which is not good, and the annealing temperature is too high, the grains on the Ohmic contact surface are easy to merge, causing the roughness of the sample surface. 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, compared with the contact resistivity. Therefore, a suitable annealing environment and effective control of the oxidation reaction are key to enhance the Ohmic contact performance.