Abstract: The free-spanning submarine pipeline has complex interaction with the surrounding soil during post-trenching, but its structural response mechanism is still not verified by physical simulation. Herein, a submarine pipeline model was designed based on the elasticity-gravity similitude law, the strain response of the whole pipeline was measured by distributed fiber optic sensors, and the physical simulation test was carried out for the post-trenching of free-spanning submarine pipelines. The test results show that the stress concentration at the mid-span and reverse bending section on both sides of the pipeline will also increase with the increasing of free span in length. In addition, two new asymmetric free spans with the mid-span and the slope shoulders on both sides as the boundary will be formed when the pipeline touches the ground in the process of post-trenching, and obvious stress release occurs at the mid-span and the reverse bending section on both sides. Since then, with the increasing of excavation length, the mid-span stress concentration of the two new free spans shifts to both ends of the pipeline. Meanwhile, the stress concentration of the reverse bending sections on both sides also shifts to both ends and tends to be stable. In general, the research results could provide a scientific reference for the treatment of free-spanning submarine pipelines.