Access to reliable and accurate bathymetric data is fundamental to many marine activities. This paper proposes a merge-normalization (MN) method that is suitable for multisource bathymetric data fusion in deep ocean areas, to solve the problem of difficult to integrate high-precision digital bathymetric model (DBM) for complex sources and various resolutions of global deep ocean bathymetric data. Then we apply it to the DBM construction of the Mariana Trench. The method combines multibeam, single-beam, and electronic navigational chart data with Shuttle Radar Topography Mission (SRTM) dataset by using the workflow of merging and normalizing, which can fill the data gaps while preserving topographic details in high-resolution bathymetric data. Compared with the widely used General Bathymetric Chart of the Oceans (GEBCO) dataset, the Mariana Trench dataset constructed in this study demonstrated improved accuracy, resolution, and topographic detail, highlighting the value of the application of the method and of its development potential.