A new method of sheet metal forming, water jet incremental sheet metal forming (WJISMF) is presented. We give the schematic illustration of WJISMF system, which includes high pressure system, NC machine, control system, water recycle system, and some attachments, and then the virtual prototype of the system is designed. To predict the whole deformation process, some simulations are carried out. Firstly, fluid structure interaction simulation for WJISMF is performed. The water jet is modeled and simulated with a computational fluid dynamics (CFD) approach, while for the material flow in the workpiece a finite element analysis (FEA) is used. Secondly, the relationship between the workpiece material deformation and nozzle diameter, and the relationship between deformation and water pressure are presented. Thirdly, the fluid structure interaction simulation model is simplified to the structure simulation model, by adopting shell 181 element and using a pressure acting on the workpiece directly instead of the CFD model. Finally, a simulation for forming a cone box is done using the simplified model. The simulation provides a powerful rationale for the practical application of WJISMF.