Abstract: Foundation treatment is an important link for large oil tank engineering. It is introduced the treatment effectiveness of 50 000 m3 oil tank foundation, which sits on soft soil and improved with stone columns. Based on the testing settlement data, settlement properties of ring wall foundation and oil tank center foundation are individually discussed during filling water preload, and Poison method is used to forecast the ultimate settlement of the ring wall foundation. Nonhomogeneos deformation at the end of water filling preload is also analyzed. All conclusions will provide a basis for the reinforcement of the oil tank foundation.