Abstract: Based on the BOTDR distributed optical fiber sensing technology, the variation laws of branch pile axial force and the action characteristic of the pile side resistance under the action of pile head loads are studied. The result shows that when the load is small, the bearing mechanism of the branch piles is similar to that of the common piles, namely with the increase of the loads, the axial forces of the branch pile are transferring gradually to the deep part. With the increasing pile head loads, the branch of the squeezed branch piles bears most of the pile head loads as the branch function of the squeezed branch piles appears gradually, but the amount of settlement and compression on the branch pile is increased, which gradually brings about the free face between the branch and its overlaying soil layer. With the in creasing settlement of the branch piles, the areas of the free face between the branch and its overlaying soil layer are gradually increased. The upper soil body of the branch is to be shear fracture under the pile-soil interaction, and gradually loses its structural properties, which generates the negative friction and subsequently increases the burdens of the branch. Thus, during the design of the branch piles we should improve the properties of the soil layer around them and the strength of pile body, and reduce compressive deformation and settlement of the branch piles so as to improve their bearing capacity.