Three-dimensional isothermal flow field of polylactic acid(PLA) of the nose transitional body of length to diameter ratio is 441 experiment with a small meshing direction twin-screw extruder head by using the PALYFLOW software. The fields of velocity, pressure, shear rate and viscosity with different process parameters are analyzed and compared. Results showed that the flow field effect become better with the increase of the screw speed and the flow rate at the appropriate temperature，but compared with the increase of the screw speed, the increase of the melt flow was more beneficial to improve mixing and plasticizing effect of the extruder head's transition flow field, and the quality of PLA products.