This paper discussed the on - site inspection on 26m deep mixing piles used as the foundation of a 50 000m3 oil tank. For the quality of project piles, the in - situ inspection methods of the standard penetration test and unconfined compression test are proposed.The test results show that the pile shaft of deep mixing piles is continuous and hard, the SPT blow count N63.5 is 21. 6 at 10 day ages, and the unconfined compression strength quis 2. 5MPa at 150 day ages. The practice testifies that the method is feasible and the oil tank project is successfully built. The paper also gives the N63.5 change at differ-ent depth, the relation of N63.5 vs- qu, E50 vs. qu modules of deformation for reference of other project.