Because of its meshless nature, the smoothed particle hydrodynamics (SPH) is ideally suitable for simulating a complex flow with a free surface and moving boundary. In this paper, we used a parallelized SPH to analyze the complex flow in a two-dimensional (2D) model of a twin screw extruder with a narrow clearance. First, in order to validate our SPH algorithm, a "forced revolving moving boundary model" previously presented by us was also used in this work. The simulation results showed good agreement with the experimental results. In addition, the flow in the full-filled 2D twin screw extruder model was simulated by using SPH and FEM, respectively. The results of both SPH and FEM showed excellent agreement. Meanwhile, we studied the squeeze flow in the intermeshing region of the 2D model in both the full-filled state and half- filled state. We found that a larger velocity scale that is far higher than the circumferential screw velocity must be applied to estimate the speed of sound. Furthermore, the effects of viscosity and gravity on the flow in the partially filled 2D twin screw extruder model were analyzed. This work laid the foundation for the accurate analysis of flow in complex geometries by using SPH.