In order to explore the mechanical characteristics of buried pipe under CLSM(controlled low strength materials) backfill, the soil-bin test was used to backfill the buried UPVC (unplasticized polyvinyl chloride) pipe with ordinary sand and CLSM respectively. By comparing and analyzing the deformation, strain and earth pressure variation around the pipe after traditional sand backfill and CLSM backfill under static load, the action law of the flexible pipe in the CLSM backfill was further clarified. The test results show as follows. Compared with sand backfill, CLSM backfill can reduce the radial deformation of the flexible pipe to a certain extent, especially the vertical deformation. After the CLSM wraps the pipe, the vertical load is mainly borne by the CLSM on the side of the pipe instead of the top, thus reducing the vertical pressure on the top of the pipe. CLSM backfill will weaken the "soil arch effect" in the area above the pipe. CLSM backfill improves the overall force of the pipe, thus significantly reducing the strain of the pipe and protecting the pipe well. These conclusion of this paper can provide theoretical guidance for the practical application of CLSM in the backfilling of buried flexible pipes.