Abstract: As the flexible composite pipelines in the shifting dune areas are easy to be suspended and displaced, it is necessary to perform a comprehensive evaluation on the safety of oil and gas pipelines to ensure their safe and stable operation. Thus, with a polyester fiber flexible reinforced composite pipeline as the example, analysis was conducted for the ultimate bearing capacity of the flexible composite pipelines under the action of suspension and lateral compression caused by the shifting sand dunes. In addition, based on the axial tensile test results, the failure process of flexible composite pipelines and the characteristic strain values under the different states of yield, reinforcement and shrinkage were identified. Combined with the finite element analysis method, the failure evaluation basis of the "ultimate slope" of suspended pipeline in the sand and the "limited displacement" of pipelines under the lateral compression of quicksand were proposed. Further, the evaluation method for flexible composite pipelines in the shifting sand areas was established, which could provide technical support for the safe operation of oil and gas pipelines in the desert areas.