Abstract: The variation of the temperature of polymer would have important influence on the injection molding process.So predicting exactly the temperature field during filling is very meaningful.3D numerical analysis of temperature field in filling stage of injection molding is investigated with the FEM method.Without the use of the Hele-Shaw approximation, the three-dimensional theoretical model and numerical scheme for temperature field were established by considering the influence of convection items in three dimensions.The energy equation was discretized using the Galerkin method.In order to keep numerical stability, the upwind method was used to handle the convection item and viscous heat item.The temperature field of the non-Newtonian and nonisothermal fluid within cavities with arbitrary thickness could be pridicted with the model.A wider range of parts was possible and the prediction results were better than the 2D or 2.5D model.The validity of the model was tested through the analysis of two cavities.