In order to predicate machined shape of electrochemical machining (ECM), a machined shape prediction method by using numerical simulation is presented in this paper. For the simulation, the mathematical model based on electric field and flow field theories firstly is built. Then the time discretization method and the finite element method (FEM) are employed to solve the mathematical model. The simulation software is developed to perform the simulation of the ECM process and predict the machined shape. Finally the method is applied in the ECM processes of the blade and the cavity. The application results show that the machined surface with high accuracy can be achieved and less test times is needed by the simulation.