In Rapid Tooling (RT), all of the forming stages influence the dimensional accuracy of the die. The forming stages include slicing the CAD model to the STL file, making the prototype using an RP machine, obtaining the ceramic mold and transforming the ceramic mold to a metal die. In RT, the precise casting that is to transform the ceramic mold to a metal die plays a very important role in the dimensional accuracy of the die. The dimensional accuracy of the casting die during the solidification process is analyzed using a three dimensional (3-D) non-linear coupled thermo-mechanical model in this paper. The material non-linearity, geometry non-linearity and boundary non-linearity during the solidification process are considered. Guaranteeing the dimensional accuracy of the casting die is a key technical problem for RT technology. The coupled thermo-mechanical analysis is used to simulate a typical cylinder part and the die of an automobile deck part. In addition, the contact model for the boundary between the casting and the matrix during the coupled thermo-mechanical analysis is analyzed using the method of contacting mechanics with the casting and the matrix treated as elastic-plastic deformable bodies. The convergence criterion and time step are selected while solving the non-linear FEM equations with the material properties changing with temperature. The numerical result for the dimensional accuracy of the automobile deck part die matches well with the experimental result. The results demonstrate that an accurate 3-D non-linear coupled thermo-mechanical FEM model can be developed to analyze the dimensional accuracy for casting dies in RT. Accurately analyzing the dimensional accuracy of the casting die has important significance for modifying the CAD model to produce a die with high dimensional accuracy. © 2001 Published by Elsevier Science B.V.