In response to the increasingly complex processes of oil testing and completion, as well as the extended cycle of running the well string, high-temperature and high-density oil testing and completion fluid is prone to sedimentation. A high solid phase can lead to reservoir damage and make wellbore cleaning more difficult. By screening various inorganic salts, organic salts, solubilizers, salt-resistant polymers, corrosion inhibitors, filter loss reducing agents, high-temperature stabilizers, and modified ultrafine barite powder as the main raw materials, a high-temperature and high-density low/solid-free oil testing and completion fluid system has been developed. Indoor experimental evaluations show that the completion fluid system exhibits good high-temperature resistance and settlement stability, strong corrosion resistance, low corrosion, and good compatibility. It can effectively address problems in deep well high-temperature, high-pressure, and high salt environments, ensuring safe and smooth well testing construction while reducing operational risks.