It is in urgent need of R & D with varying ellipse machining lathe for high power marine diesel engine piston, which are imperative in important economic areas, such as large vessels, heavy motorcycle, automotive, aerospace and construction machinery, and others in China. A special fixture using for the processing of large diameter piston lathe was designed, and its three-dimensional (3-D) modeling and finite element simulation analysis (FEA) were carried out. It is proved that the rational design of the fixture can meet the work requirements.