Borehole cast-in-place piles have many advantages,such as high bearing capacity of single pile,no noise with construction,no special equipment needed and so on. According to these, they have been widely accepted to foundation engineering. But this technique is much reliable to its construction method, hydrogeological and engineering geological condisions. If it is not considered any factor to use this technique, it must resulted in harmfulness. Based on analyzing the foundation settlement with Borehole cast-in-place piles of a seven-floor structure in Lanzhou, which is built on subsidence loess and man-filled soil,treating method of this harmfulness and its engineering practice are introduced.