Solidworks 3D modeling software was used to establish the physical model of co-rotating twin-screw and counter-rotating twin-screw. By using Polyflow, polylactic acid fluid was analyzed in 3D fluid simulation. The pro- cessing effects of screw elements of counter-rotating and co-rotating twin-screw extruder on polylactic acid fluid were studied by comparing shear rate field, viscosity field, pressure field and velocity field of polylactic acid fluid. The results showed that with high average shear rate and slow axial motion of polylactic acid fluids in screw elements of co-rotating twin screw extruder, a better mixing effect was achieved, while the faster axial velocity of polylactic acid fluid in screw element of counter-rotating twin-screw extruder led to a better extrusion effect.