Freservoir in Y Oilfield is characterized with high temperature, high pressure and high yield with corrosive fluids. In order to ensure a long term, efficient and safe production, it is necessary to study the well completion technology and anticorrosion for string protection. The completion string with packer is run downhole, and the annulus between tubing and casing above packer is then filled with anticorrosion packer fluid. Two introduced annulus packer fluid systems are tested at lab to evaluate the physical and chemical properties of , high temperature stability, and the corrosion of pipe downhole. Test results show that CaCl2 annulus packer fluid has poor high temperature stability, the high values of immersion corrosion rate values and galvanic corrosion rate values are 0.062 mm/a and 0.078 mm/a respectively, larger than the set corrosion rate of 0.05 mm/a. While the introduced NaCl KCl annulus packer fluid has better high temperature stability with high values of immersion corrosion rate values and galvanic corrosion rate values 0.014 mm/a and 0.037 mm/a respectively, lower than the set corrosion rate of 0.05 mm/a. In view of this situation, the improvement and optimizing design are made on this introduced CaCl2 annulus packer fluid to determine the proper system. The optimizing designed CaCl2 annulus packer fluid shows good high temperature stability, the immersion corrosion and galvanic corrosion rate values are below the set corrosion rate, and the overall performance have reached the field application requirements.