Abstract: In order to meet the requirements of properties including high temperature resistance, high density, low corrosion rate, and reservoir protection, etc. for completion fluids under harsh working conditions in a high-temperature and high-pressure well in the South China Sea, the ratio of high valency metal salt ions was optimized to regulate the crystallization point and density gradient of the solution, and a high temperature-resistant, high-density, and solid-free completion fluid system was constructed. Through methods such as high-temperature aging experiments, corrosion testing, and permeability recovery testing, the key properties of the completion fluid, such as density stability, hydrate inhibition, corrosion rate, and reservoir protection, were tested. The results show that the density of the high-density and solid-free completion fluid can reach up to 1.85 kg/L. After aging at a temperature of 170 °C for 3 days, the density fluctuation was only 0.01 kg/L, indicating good natural gas hydrate inhibition performance and a crystallization temperature of less than −12.5 °C. The density change rate of the completion fluid under high-temperature and high-pressure conditions was only 3.8%. The corrosion rate was less than 0.076 mm/a, meeting the industry standard requirements. The average core permeability recovery value reached 87.94%. The field application has verified the effectiveness of the solid-free completion fluid in controlling the water lock effect, hydrate inhibition, and maintaining wellbore integrity. After the application of the completion fluid, positive production increase response was observed, and the actual gas production rate reached 133% of the design capacity. This solid-free completion fluid provides a new technical solution for high-temperature and high-pressure oil and gas field completion operations.