Welding is the most important work of steel structure construction in ocean engineering project,and the welding qualification rate is the key problem of construction. Welding defects will lead to repair,and the repair will not only delay the construction period and increase the project cost,but also will have a certain impact on the performance of the welded joint. Through the analysis with fishbone diagram,we concluded that the main reason for the welding defect is the welder itself. Most of the welding defects are due to the welders who welded not in accordance with the welding process which was specified by project. Regularly calculating the welding qualification rate,and punishing the welders who with a low welding qualification rate,which can effectively make the welders more conscientious in their welding work,thus reducing the welding defects.