Aiming at the serious problem of gradual failure and destruction of pipelines caused by surface settlement in karst areas, finite element analysis software is used to analyze the mechanical response of the pipeline under different internal pressures and different settlement lengths under the limit displacement state of the pipeline, and analyzes under different internal pressures The limit suspended length of the pipeline, the warning displacement under the limit displacement and the limit suspended length of the pipeline and the different settlement length under different conditions are obtained, which provides the basis for the pipeline safety warning and safety evaluation. The results show that with the increase of the subsidence length, the dangerous position of the pipeline shifts from mid-span to both ends, and the mid-span stress decreases continuously while the stress at both ends increases gradually. With the increase of internal pressure, the subsidence length of the pipeline is shorter when the dangerous position appears at both ends. The larger the internal pressure is, the larger the maximum displacement and warning of the pipeline is, the shorter the limit suspension length of the pipeline is.