This paper presents a new method of dieless sheet metal forming, water jet incremental sheet metal forming (WJISMF). A five-axis WJISMF machine was designed based on this technology. The machine has five degrees of freedom (DOF) including two rotational DOF of the nozzle and three translational DOF of the workbench. It has good flexibility and can be used for low cost production of prototype. The paper introduces the subsystems of WJISMF system. In addition, a new simulation method for the forming process is given, in which the complex simulation about fluid-structure interaction is simplified by loading equivalent pressure. The effect of water jet pressure and sheet thickness on the metal forming accuracy is evaluated by simulation analysis respectively.