The horizontal directional drilling (HDD) technology, as one of the core technologies in the trenchless field, has formed a mature application system for the small-diameter pipelines below DN300. Taking an emergency drainage project of a barrier lake as an example, to meet the drainage flow requirement equivalent to DN1200 pipe diameter, a DN600 dual-pipe parallel laying scheme is innovatively proposed. By achieving the equivalent flow of large pipes through dual-pipe parallelism, the application bottleneck of traditional HDD technology in large-pipe diameter scenarios is broken through. The engineering practice demonstrates that this scheme not only meets the drainage flow requirements, but also has the advantages including strong technical feasibility, low construction difficulty, and excellent cost-effectiveness, which provides the innovative ideas for the application of HDD technology in the field of drainage and offers the theoretical support and practical reference for the expansion and optimization of trenchless technology.