A new numerical scheme for simulating the filling stage of injection molding has been presented in this paper. The algorithm is based on isothermal, incompressible, generalized Hele-Shaw flow of a viscous fluid. The governing equation involving the pressure field and fill factor which tracks the location of the front surface is developed and solved in an iterative manner. The present methodology has no time step restrictions based on the Courant conditions that exist in the traditional finite element/control volume (FE/CV) type formulations. As a result, the efficiency of the filling simulation is significantly improved. Examples provided verify the proposed methodology.