Abstract: Based on the bending prototype tests on the thin-wall steel and spun concrete composite piles (TSC pile) 800 mm in diameter, the applicability of the existing ordinary TSC pile theory to large-diameter TSC piles is verified, and the relationship between the steel ratio and the ultimate bearing capacity is preliminarily studied. The bending test results show that the ordinary TSC pile theory can be basically applied to the large-diameter TSC piles. Whereas the impact analysis of the steel ratio indicats that a linear relationship between the steel ratio and the ultimate flexural capacity can be concluded within a small range, which shows that the ultimate flexural capacity of TSC piles can be improved by increasing the steel ratio.