The installation technologies for large-scale box culverts adopted in the artificial island of Hong Kong-Zhuhai-Macao Bridge-Hong Kong Boundary Crossing Facilities（HKBCF）are sectional prefabrication and floating transport. To avoid the leakage of box culverts during floating transport，we carry out structural design，calculation，and verification for the leakproof structure of box culverts（with steel seal doors）and optimize the leakproof structure on the basis of watertightness tests. The result shows that the above sealing technology is feasible，and no seepage or leakage is reported for 29 sections of prefabricated box culverts during floating transport. Moreover，the technology significantly improves the construction efficiency and reduces the construction cost，which may serve as a reference for similar projects.