By taking the line type optimization of low-speed full ship as the research object, some key issues are deeply researched. The approximate model method is applied to the hull form optimization, the complex and time-consuming CFD numerical calculation in the optimization process is replaced by the approximate model established with a limited number of high-precision CFD calculation results, and the multidisciplinary comprehensive optimization platform for marine hydrodynamic performance developed by the team is used to complete and verify the line type optimization of deadweight tonnage 46 000 t oil tanker.