Based on BOTDR distributed optical fiber sensing technology, this paper studies the variation law of branch pile axial force under the action of pile head loads and the action characteristic of pile side resistance during static load test. The result shows that: the branch of squeezed branch pile, as the major load-carrying object, bears most of the pile head loads and its function gradually emerges with increasing pile head loads. Under the action of pile head loads, the settlement and compression value of branch pile is elevated, which gradually brings about free face between branch and its overlaying soil layer. When the load exceed certain amount, the overlaying soil body of branch cracks under pile-soil interaction, and gradually loses its structural properties, because of which its settlement emerges and negative friction subsequently generated. Thus, during the design of branch pile, one should improve the properties of the soil layer around branch pile, enhance the strength of pile shaft, and lessen pile compressing deformation and settlement, so as to elevate the bearing capacity of branch pile.