For a large-diameter double-insulating submarine pipeline located in Liaodong Bay, a span across channels is treated and subsidence protection is achieved during on-stream maintenance. Test results after the construction show that the subsidence depth reaches 4.5 m, which is the largest depth compared with other projects in China. In the subsequent rock dumping protection, trench soil is used to finish the first backfill layer, which can save the cost and greatly promote the construction efficiency. The design and construction methods used in this project are of value for further design of similar submarine pipeline projects.