Abstract: How the metal flows in the extending cavity during continuous extruding/extending forming in semi-solid state was simulated by finite element method (FEM) to investigate the metal flow behavior in the moulds designed with different parameters. The calculated results indicate that the highly solidifiable semi-solid alloy fills in the extending mould in form of laminar flow and the flow velocity decreases gradually from the center to all sides in mould. The flow velocity at the outlet of mould becomes more even with increasing extending angle or step length. However, The flow velocity at the outlet of mould becomes more uneven with increasing outlet width. There is a dead zone or vortex flow on both sides of mould when the step is too long. It is proved that the continuous extruding/extending forming can be implemented only if the mould is designed rationally.