Abstract: With regard to the situation that the high-speed railway has requirements of strict post-construction settlement and the researches on the additional settlement of pile foundation caused by soils immersion are inadequate in collapsible loess area. Based on the field results of large pile immersion tests, the mechanism of the additional settlement of piles caused by soils immersion is studied, and a model is proposed. A method for calculating the post-construction settlement of pile foundation of bridges of high speed railway in collapsible loess area is put forward. The results show that the post-construction settlement of pile foundation of bridges should mainly consider the additional settlement caused by soil immersion in collapsible loess area, which mainly reflected by the compression of pile shaft and is much larger than the settlement only caused by structure load. The creep of concrete should not be neglected in the settlement calculation. The distribution of axial force of piles before soil immersion can be calculated using the load transfer theory, and that after soil immersion also can be obtained if assuming the pile side and pile end resistances develop synchronously. Thereafter, the elastic compression of pile shaft, creep deformation of concrete, and pile tip settlement, which contribute to the post-construction settlement, can be calculated separately.