Abstract: In soft soil area it is necessary to take use of mud protection in the forming process of cast-in-situ bored piles. Based on the measured data of cast-in-situ bored piles of a high-rise residential in Pudong District of Shanghai, the influence of two kinds of mud circulations on the diameter of pile hole is studied, and its mechanism is discussed. The results show that in Shanghai, the soft soil area, the normal mud circulation rather than the reverse mud circulation can increase the roughness of hole wall and expand the diameter of pile hole to some extent, and it plays a role in increasing the bearing capacity of the piles.