Objective: The flow channel distribution of polylactic acid （PLA） in different groove depths of a double screw extruder was discussed. Methods: Three kinds of screw elements with different depth of screw groove and their corresponding flow channel models were established by Solidworks software. Polyflow fluid simulation software was used for numerical simulation, and FieldView software was used for numerical analysis of post-processing results. The pressure field, shear rate field, viscosity field and residence time distribution curve （RTD） of polylactic acid （PLA） in three different screw extruders with different groove depths were studied. Results: The depth of the screw groove was changed by changing the diameter of the root circle of the screw element and the corresponding diameter of the flow channel. Under the same condition, the shallower the depth of the screw groove, the greater the fluctuation of pressure and shear rate, but the smaller the fluctuation of viscosity. The deeper the screw groove, the higher the axial mixing performance. Conclusion: The change of screw groove depth has influence on the mixing performance of flow field and has certain regularity. The twin-screw extruder with comprehensive mixing performance can be selected according to the experiment for practical production.